xref: /petsc/src/mat/impls/sbaij/seq/sbaijfact2.c (revision ccb4e88a40f0b86eaeca07ff64c64e4de2fae686)
1 
2 /*
3     Factorization code for SBAIJ format.
4 */
5 
6 #include <../src/mat/impls/sbaij/seq/sbaij.h>
7 #include <../src/mat/impls/baij/seq/baij.h>
8 #include <petsc/private/kernels/blockinvert.h>
9 
10 PetscErrorCode MatSolve_SeqSBAIJ_N_inplace(Mat A,Vec bb,Vec xx)
11 {
12   Mat_SeqSBAIJ      *a   =(Mat_SeqSBAIJ*)A->data;
13   IS                isrow=a->row;
14   PetscInt          mbs  =a->mbs,*ai=a->i,*aj=a->j;
15   PetscErrorCode    ierr;
16   const PetscInt    *r;
17   PetscInt          nz,*vj,k,idx,k1;
18   PetscInt          bs =A->rmap->bs,bs2 = a->bs2;
19   const MatScalar   *aa=a->a,*v,*diag;
20   PetscScalar       *x,*xk,*xj,*xk_tmp,*t;
21   const PetscScalar *b;
22 
23   PetscFunctionBegin;
24   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
25   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
26   t    = a->solve_work;
27   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
28   ierr = PetscMalloc1(bs,&xk_tmp);CHKERRQ(ierr);
29 
30   /* solve U^T * D * y = b by forward substitution */
31   xk = t;
32   for (k=0; k<mbs; k++) { /* t <- perm(b) */
33     idx = bs*r[k];
34     for (k1=0; k1<bs; k1++) *xk++ = b[idx+k1];
35   }
36   for (k=0; k<mbs; k++) {
37     v    = aa + bs2*ai[k];
38     xk   = t + k*bs;    /* Dk*xk = k-th block of x */
39     ierr = PetscArraycpy(xk_tmp,xk,bs);CHKERRQ(ierr); /* xk_tmp <- xk */
40     nz   = ai[k+1] - ai[k];
41     vj   = aj + ai[k];
42     xj   = t + (*vj)*bs; /* *vj-th block of x, *vj>k */
43     while (nz--) {
44       /* x(:) += U(k,:)^T*(Dk*xk) */
45       PetscKernel_v_gets_v_plus_Atranspose_times_w(bs,xj,v,xk_tmp); /* xj <- xj + v^t * xk */
46       vj++; xj = t + (*vj)*bs;
47       v       += bs2;
48     }
49     /* xk = inv(Dk)*(Dk*xk) */
50     diag = aa+k*bs2;                            /* ptr to inv(Dk) */
51     PetscKernel_w_gets_A_times_v(bs,xk_tmp,diag,xk); /* xk <- diag * xk */
52   }
53 
54   /* solve U*x = y by back substitution */
55   for (k=mbs-1; k>=0; k--) {
56     v  = aa + bs2*ai[k];
57     xk = t + k*bs;        /* xk */
58     nz = ai[k+1] - ai[k];
59     vj = aj + ai[k];
60     xj = t + (*vj)*bs;
61     while (nz--) {
62       /* xk += U(k,:)*x(:) */
63       PetscKernel_v_gets_v_plus_A_times_w(bs,xk,v,xj); /* xk <- xk + v*xj */
64       vj++;
65       v += bs2; xj = t + (*vj)*bs;
66     }
67     idx = bs*r[k];
68     for (k1=0; k1<bs; k1++) x[idx+k1] = *xk++;
69   }
70 
71   ierr = PetscFree(xk_tmp);CHKERRQ(ierr);
72   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
73   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
74   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
75   ierr = PetscLogFlops(4.0*bs2*a->nz -(bs+2.0*bs2)*mbs);CHKERRQ(ierr);
76   PetscFunctionReturn(0);
77 }
78 
79 PetscErrorCode MatForwardSolve_SeqSBAIJ_N_inplace(Mat A,Vec bb,Vec xx)
80 {
81   PetscFunctionBegin;
82   SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"not implemented yet");
83 }
84 
85 PetscErrorCode MatBackwardSolve_SeqSBAIJ_N_inplace(Mat A,Vec bb,Vec xx)
86 {
87   PetscFunctionBegin;
88   SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Not yet implemented");
89 }
90 
91 PetscErrorCode MatForwardSolve_SeqSBAIJ_N_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscInt bs,PetscScalar *x)
92 {
93   PetscErrorCode  ierr;
94   PetscInt        nz,k;
95   const PetscInt  *vj,bs2 = bs*bs;
96   const MatScalar *v,*diag;
97   PetscScalar     *xk,*xj,*xk_tmp;
98 
99   PetscFunctionBegin;
100   ierr = PetscMalloc1(bs,&xk_tmp);CHKERRQ(ierr);
101   for (k=0; k<mbs; k++) {
102     v    = aa + bs2*ai[k];
103     xk   = x + k*bs;    /* Dk*xk = k-th block of x */
104     ierr = PetscArraycpy(xk_tmp,xk,bs);CHKERRQ(ierr); /* xk_tmp <- xk */
105     nz   = ai[k+1] - ai[k];
106     vj   = aj + ai[k];
107     xj   = x + (*vj)*bs; /* *vj-th block of x, *vj>k */
108     while (nz--) {
109       /* x(:) += U(k,:)^T*(Dk*xk) */
110       PetscKernel_v_gets_v_plus_Atranspose_times_w(bs,xj,v,xk_tmp); /* xj <- xj + v^t * xk */
111       vj++; xj = x + (*vj)*bs;
112       v       += bs2;
113     }
114     /* xk = inv(Dk)*(Dk*xk) */
115     diag = aa+k*bs2;                            /* ptr to inv(Dk) */
116     PetscKernel_w_gets_A_times_v(bs,xk_tmp,diag,xk); /* xk <- diag * xk */
117   }
118   ierr = PetscFree(xk_tmp);CHKERRQ(ierr);
119   PetscFunctionReturn(0);
120 }
121 
122 PetscErrorCode MatBackwardSolve_SeqSBAIJ_N_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscInt bs,PetscScalar *x)
123 {
124   PetscInt        nz,k;
125   const PetscInt  *vj,bs2 = bs*bs;
126   const MatScalar *v;
127   PetscScalar     *xk,*xj;
128 
129   PetscFunctionBegin;
130   for (k=mbs-1; k>=0; k--) {
131     v  = aa + bs2*ai[k];
132     xk = x + k*bs;        /* xk */
133     nz = ai[k+1] - ai[k];
134     vj = aj + ai[k];
135     xj = x + (*vj)*bs;
136     while (nz--) {
137       /* xk += U(k,:)*x(:) */
138       PetscKernel_v_gets_v_plus_A_times_w(bs,xk,v,xj); /* xk <- xk + v*xj */
139       vj++;
140       v += bs2; xj = x + (*vj)*bs;
141     }
142   }
143   PetscFunctionReturn(0);
144 }
145 
146 PetscErrorCode MatSolve_SeqSBAIJ_N_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
147 {
148   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
149   PetscErrorCode    ierr;
150   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
151   PetscInt          bs =A->rmap->bs;
152   const MatScalar   *aa=a->a;
153   PetscScalar       *x;
154   const PetscScalar *b;
155 
156   PetscFunctionBegin;
157   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
158   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
159 
160   /* solve U^T * D * y = b by forward substitution */
161   ierr = PetscArraycpy(x,b,bs*mbs);CHKERRQ(ierr); /* x <- b */
162   ierr = MatForwardSolve_SeqSBAIJ_N_NaturalOrdering(ai,aj,aa,mbs,bs,x);CHKERRQ(ierr);
163 
164   /* solve U*x = y by back substitution */
165   ierr = MatBackwardSolve_SeqSBAIJ_N_NaturalOrdering(ai,aj,aa,mbs,bs,x);CHKERRQ(ierr);
166 
167   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
168   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
169   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
170   PetscFunctionReturn(0);
171 }
172 
173 PetscErrorCode MatForwardSolve_SeqSBAIJ_N_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
174 {
175   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
176   PetscErrorCode    ierr;
177   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
178   PetscInt          bs =A->rmap->bs;
179   const MatScalar   *aa=a->a;
180   const PetscScalar *b;
181   PetscScalar       *x;
182 
183   PetscFunctionBegin;
184   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
185   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
186   ierr = PetscArraycpy(x,b,bs*mbs);CHKERRQ(ierr); /* x <- b */
187   ierr = MatForwardSolve_SeqSBAIJ_N_NaturalOrdering(ai,aj,aa,mbs,bs,x);CHKERRQ(ierr);
188   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
189   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
190   ierr = PetscLogFlops(2.0*a->bs2*a->nz - bs*mbs);CHKERRQ(ierr);
191   PetscFunctionReturn(0);
192 }
193 
194 PetscErrorCode MatBackwardSolve_SeqSBAIJ_N_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
195 {
196   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
197   PetscErrorCode    ierr;
198   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
199   PetscInt          bs =A->rmap->bs;
200   const MatScalar   *aa=a->a;
201   const PetscScalar *b;
202   PetscScalar       *x;
203 
204   PetscFunctionBegin;
205   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
206   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
207   ierr = PetscArraycpy(x,b,bs*mbs);CHKERRQ(ierr);
208   ierr = MatBackwardSolve_SeqSBAIJ_N_NaturalOrdering(ai,aj,aa,mbs,bs,x);CHKERRQ(ierr);
209   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
210   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
211   ierr = PetscLogFlops(2.0*a->bs2*(a->nz-mbs));CHKERRQ(ierr);
212   PetscFunctionReturn(0);
213 }
214 
215 PetscErrorCode MatSolve_SeqSBAIJ_7_inplace(Mat A,Vec bb,Vec xx)
216 {
217   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
218   IS                isrow=a->row;
219   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j,*r,*vj;
220   PetscErrorCode    ierr;
221   PetscInt          nz,k,idx;
222   const MatScalar   *aa=a->a,*v,*d;
223   PetscScalar       *x,x0,x1,x2,x3,x4,x5,x6,*t,*tp;
224   const PetscScalar *b;
225 
226   PetscFunctionBegin;
227   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
228   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
229   t    = a->solve_work;
230   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
231 
232   /* solve U^T * D * y = b by forward substitution */
233   tp = t;
234   for (k=0; k<mbs; k++) { /* t <- perm(b) */
235     idx   = 7*r[k];
236     tp[0] = b[idx];
237     tp[1] = b[idx+1];
238     tp[2] = b[idx+2];
239     tp[3] = b[idx+3];
240     tp[4] = b[idx+4];
241     tp[5] = b[idx+5];
242     tp[6] = b[idx+6];
243     tp   += 7;
244   }
245 
246   for (k=0; k<mbs; k++) {
247     v  = aa + 49*ai[k];
248     vj = aj + ai[k];
249     tp = t + k*7;
250     x0 =tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4]; x5=tp[5]; x6=tp[6];
251     nz = ai[k+1] - ai[k];
252     tp = t + (*vj)*7;
253     while (nz--) {
254       tp[0]+=  v[0]*x0 +  v[1]*x1 +  v[2]*x2 + v[3]*x3 + v[4]*x4 + v[5]*x5 + v[6]*x6;
255       tp[1]+=  v[7]*x0 +  v[8]*x1 +  v[9]*x2+ v[10]*x3+ v[11]*x4+ v[12]*x5+ v[13]*x6;
256       tp[2]+= v[14]*x0 + v[15]*x1 + v[16]*x2+ v[17]*x3+ v[18]*x4+ v[19]*x5+ v[20]*x6;
257       tp[3]+= v[21]*x0 + v[22]*x1 + v[23]*x2+ v[24]*x3+ v[25]*x4+ v[26]*x5+ v[27]*x6;
258       tp[4]+= v[28]*x0 + v[29]*x1 + v[30]*x2+ v[31]*x3+ v[32]*x4+ v[33]*x5+ v[34]*x6;
259       tp[5]+= v[35]*x0 + v[36]*x1 + v[37]*x2+ v[38]*x3+ v[39]*x4+ v[40]*x5+ v[41]*x6;
260       tp[6]+= v[42]*x0 + v[43]*x1 + v[44]*x2+ v[45]*x3+ v[46]*x4+ v[47]*x5+ v[48]*x6;
261       vj++;
262       tp = t + (*vj)*7;
263       v += 49;
264     }
265 
266     /* xk = inv(Dk)*(Dk*xk) */
267     d     = aa+k*49;       /* ptr to inv(Dk) */
268     tp    = t + k*7;
269     tp[0] = d[0]*x0 + d[7]*x1 + d[14]*x2 + d[21]*x3 + d[28]*x4 + d[35]*x5 + d[42]*x6;
270     tp[1] = d[1]*x0 + d[8]*x1 + d[15]*x2 + d[22]*x3 + d[29]*x4 + d[36]*x5 + d[43]*x6;
271     tp[2] = d[2]*x0 + d[9]*x1 + d[16]*x2 + d[23]*x3 + d[30]*x4 + d[37]*x5 + d[44]*x6;
272     tp[3] = d[3]*x0+ d[10]*x1 + d[17]*x2 + d[24]*x3 + d[31]*x4 + d[38]*x5 + d[45]*x6;
273     tp[4] = d[4]*x0+ d[11]*x1 + d[18]*x2 + d[25]*x3 + d[32]*x4 + d[39]*x5 + d[46]*x6;
274     tp[5] = d[5]*x0+ d[12]*x1 + d[19]*x2 + d[26]*x3 + d[33]*x4 + d[40]*x5 + d[47]*x6;
275     tp[6] = d[6]*x0+ d[13]*x1 + d[20]*x2 + d[27]*x3 + d[34]*x4 + d[41]*x5 + d[48]*x6;
276   }
277 
278   /* solve U*x = y by back substitution */
279   for (k=mbs-1; k>=0; k--) {
280     v  = aa + 49*ai[k];
281     vj = aj + ai[k];
282     tp = t + k*7;
283     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4]; x5=tp[5];  x6=tp[6]; /* xk */
284     nz = ai[k+1] - ai[k];
285 
286     tp = t + (*vj)*7;
287     while (nz--) {
288       /* xk += U(k,:)*x(:) */
289       x0 += v[0]*tp[0] + v[7]*tp[1] + v[14]*tp[2] + v[21]*tp[3] + v[28]*tp[4] + v[35]*tp[5] + v[42]*tp[6];
290       x1 += v[1]*tp[0] + v[8]*tp[1] + v[15]*tp[2] + v[22]*tp[3] + v[29]*tp[4] + v[36]*tp[5] + v[43]*tp[6];
291       x2 += v[2]*tp[0] + v[9]*tp[1] + v[16]*tp[2] + v[23]*tp[3] + v[30]*tp[4] + v[37]*tp[5] + v[44]*tp[6];
292       x3 += v[3]*tp[0]+ v[10]*tp[1] + v[17]*tp[2] + v[24]*tp[3] + v[31]*tp[4] + v[38]*tp[5] + v[45]*tp[6];
293       x4 += v[4]*tp[0]+ v[11]*tp[1] + v[18]*tp[2] + v[25]*tp[3] + v[32]*tp[4] + v[39]*tp[5] + v[46]*tp[6];
294       x5 += v[5]*tp[0]+ v[12]*tp[1] + v[19]*tp[2] + v[26]*tp[3] + v[33]*tp[4] + v[40]*tp[5] + v[47]*tp[6];
295       x6 += v[6]*tp[0]+ v[13]*tp[1] + v[20]*tp[2] + v[27]*tp[3] + v[34]*tp[4] + v[41]*tp[5] + v[48]*tp[6];
296       vj++;
297       tp = t + (*vj)*7;
298       v += 49;
299     }
300     tp       = t + k*7;
301     tp[0]    = x0; tp[1]=x1; tp[2]=x2; tp[3]=x3; tp[4]=x4; tp[5]=x5; tp[6]=x6;
302     idx      = 7*r[k];
303     x[idx]   = x0;
304     x[idx+1] = x1;
305     x[idx+2] = x2;
306     x[idx+3] = x3;
307     x[idx+4] = x4;
308     x[idx+5] = x5;
309     x[idx+6] = x6;
310   }
311 
312   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
313   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
314   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
315   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
316   PetscFunctionReturn(0);
317 }
318 
319 PetscErrorCode MatForwardSolve_SeqSBAIJ_7_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
320 {
321   const MatScalar *v,*d;
322   PetscScalar     *xp,x0,x1,x2,x3,x4,x5,x6;
323   PetscInt        nz,k;
324   const PetscInt  *vj;
325 
326   PetscFunctionBegin;
327   for (k=0; k<mbs; k++) {
328     v  = aa + 49*ai[k];
329     xp = x + k*7;
330     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4]; x5=xp[5]; x6=xp[6]; /* Dk*xk = k-th block of x */
331     nz = ai[k+1] - ai[k];
332     vj = aj + ai[k];
333     xp = x + (*vj)*7;
334     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
335     PetscPrefetchBlock(v+49*nz,49*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
336     while (nz--) {
337       /* x(:) += U(k,:)^T*(Dk*xk) */
338       xp[0]+=  v[0]*x0 +  v[1]*x1 +  v[2]*x2 + v[3]*x3 + v[4]*x4 + v[5]*x5 + v[6]*x6;
339       xp[1]+=  v[7]*x0 +  v[8]*x1 +  v[9]*x2+ v[10]*x3+ v[11]*x4+ v[12]*x5+ v[13]*x6;
340       xp[2]+= v[14]*x0 + v[15]*x1 + v[16]*x2+ v[17]*x3+ v[18]*x4+ v[19]*x5+ v[20]*x6;
341       xp[3]+= v[21]*x0 + v[22]*x1 + v[23]*x2+ v[24]*x3+ v[25]*x4+ v[26]*x5+ v[27]*x6;
342       xp[4]+= v[28]*x0 + v[29]*x1 + v[30]*x2+ v[31]*x3+ v[32]*x4+ v[33]*x5+ v[34]*x6;
343       xp[5]+= v[35]*x0 + v[36]*x1 + v[37]*x2+ v[38]*x3+ v[39]*x4+ v[40]*x5+ v[41]*x6;
344       xp[6]+= v[42]*x0 + v[43]*x1 + v[44]*x2+ v[45]*x3+ v[46]*x4+ v[47]*x5+ v[48]*x6;
345       vj++;
346       xp = x + (*vj)*7;
347       v += 49;
348     }
349     /* xk = inv(Dk)*(Dk*xk) */
350     d     = aa+k*49;       /* ptr to inv(Dk) */
351     xp    = x + k*7;
352     xp[0] = d[0]*x0 + d[7]*x1 + d[14]*x2 + d[21]*x3 + d[28]*x4 + d[35]*x5 + d[42]*x6;
353     xp[1] = d[1]*x0 + d[8]*x1 + d[15]*x2 + d[22]*x3 + d[29]*x4 + d[36]*x5 + d[43]*x6;
354     xp[2] = d[2]*x0 + d[9]*x1 + d[16]*x2 + d[23]*x3 + d[30]*x4 + d[37]*x5 + d[44]*x6;
355     xp[3] = d[3]*x0+ d[10]*x1 + d[17]*x2 + d[24]*x3 + d[31]*x4 + d[38]*x5 + d[45]*x6;
356     xp[4] = d[4]*x0+ d[11]*x1 + d[18]*x2 + d[25]*x3 + d[32]*x4 + d[39]*x5 + d[46]*x6;
357     xp[5] = d[5]*x0+ d[12]*x1 + d[19]*x2 + d[26]*x3 + d[33]*x4 + d[40]*x5 + d[47]*x6;
358     xp[6] = d[6]*x0+ d[13]*x1 + d[20]*x2 + d[27]*x3 + d[34]*x4 + d[41]*x5 + d[48]*x6;
359   }
360   PetscFunctionReturn(0);
361 }
362 
363 PetscErrorCode MatBackwardSolve_SeqSBAIJ_7_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
364 {
365   const MatScalar *v;
366   PetscScalar     *xp,x0,x1,x2,x3,x4,x5,x6;
367   PetscInt        nz,k;
368   const PetscInt  *vj;
369 
370   PetscFunctionBegin;
371   for (k=mbs-1; k>=0; k--) {
372     v  = aa + 49*ai[k];
373     xp = x + k*7;
374     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4]; x5=xp[5]; x6=xp[6]; /* xk */
375     nz = ai[k+1] - ai[k];
376     vj = aj + ai[k];
377     xp = x + (*vj)*7;
378     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
379     PetscPrefetchBlock(v-49*nz,49*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
380     while (nz--) {
381       /* xk += U(k,:)*x(:) */
382       x0 += v[0]*xp[0] + v[7]*xp[1] + v[14]*xp[2] + v[21]*xp[3] + v[28]*xp[4] + v[35]*xp[5] + v[42]*xp[6];
383       x1 += v[1]*xp[0] + v[8]*xp[1] + v[15]*xp[2] + v[22]*xp[3] + v[29]*xp[4] + v[36]*xp[5] + v[43]*xp[6];
384       x2 += v[2]*xp[0] + v[9]*xp[1] + v[16]*xp[2] + v[23]*xp[3] + v[30]*xp[4] + v[37]*xp[5] + v[44]*xp[6];
385       x3 += v[3]*xp[0]+ v[10]*xp[1] + v[17]*xp[2] + v[24]*xp[3] + v[31]*xp[4] + v[38]*xp[5] + v[45]*xp[6];
386       x4 += v[4]*xp[0]+ v[11]*xp[1] + v[18]*xp[2] + v[25]*xp[3] + v[32]*xp[4] + v[39]*xp[5] + v[46]*xp[6];
387       x5 += v[5]*xp[0]+ v[12]*xp[1] + v[19]*xp[2] + v[26]*xp[3] + v[33]*xp[4] + v[40]*xp[5] + v[47]*xp[6];
388       x6 += v[6]*xp[0]+ v[13]*xp[1] + v[20]*xp[2] + v[27]*xp[3] + v[34]*xp[4] + v[41]*xp[5] + v[48]*xp[6];
389       vj++;
390       v += 49; xp = x + (*vj)*7;
391     }
392     xp   = x + k*7;
393     xp[0]=x0; xp[1]=x1; xp[2]=x2; xp[3]=x3; xp[4]=x4; xp[5]=x5; xp[6]=x6;
394   }
395   PetscFunctionReturn(0);
396 }
397 
398 PetscErrorCode MatSolve_SeqSBAIJ_7_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
399 {
400   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
401   PetscErrorCode    ierr;
402   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
403   const MatScalar   *aa=a->a;
404   PetscScalar       *x;
405   const PetscScalar *b;
406 
407   PetscFunctionBegin;
408   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
409   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
410 
411   /* solve U^T * D * y = b by forward substitution */
412   ierr = PetscArraycpy(x,b,7*mbs);CHKERRQ(ierr); /* x <- b */
413   ierr = MatForwardSolve_SeqSBAIJ_7_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
414 
415   /* solve U*x = y by back substitution */
416   ierr = MatBackwardSolve_SeqSBAIJ_7_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
417 
418   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
419   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
420   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
421   PetscFunctionReturn(0);
422 }
423 
424 PetscErrorCode MatForwardSolve_SeqSBAIJ_7_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
425 {
426   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
427   PetscErrorCode    ierr;
428   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
429   const MatScalar   *aa=a->a;
430   PetscScalar       *x;
431   const PetscScalar *b;
432 
433   PetscFunctionBegin;
434   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
435   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
436   ierr = PetscArraycpy(x,b,7*mbs);CHKERRQ(ierr);
437   ierr = MatForwardSolve_SeqSBAIJ_7_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
438   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
439   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
440   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
441   PetscFunctionReturn(0);
442 }
443 
444 PetscErrorCode MatBackwardSolve_SeqSBAIJ_7_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
445 {
446   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
447   PetscErrorCode    ierr;
448   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
449   const MatScalar   *aa=a->a;
450   PetscScalar       *x;
451   const PetscScalar *b;
452 
453   PetscFunctionBegin;
454   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
455   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
456   ierr = PetscArraycpy(x,b,7*mbs);CHKERRQ(ierr);
457   ierr = MatBackwardSolve_SeqSBAIJ_7_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
458   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
459   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
460   ierr = PetscLogFlops(2.0*a->bs2*(a->nz-mbs));CHKERRQ(ierr);
461   PetscFunctionReturn(0);
462 }
463 
464 PetscErrorCode MatSolve_SeqSBAIJ_6_inplace(Mat A,Vec bb,Vec xx)
465 {
466   Mat_SeqSBAIJ      *a   =(Mat_SeqSBAIJ*)A->data;
467   IS                isrow=a->row;
468   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j,*r,*vj;
469   PetscErrorCode    ierr;
470   PetscInt          nz,k,idx;
471   const MatScalar   *aa=a->a,*v,*d;
472   PetscScalar       *x,x0,x1,x2,x3,x4,x5,*t,*tp;
473   const PetscScalar *b;
474 
475   PetscFunctionBegin;
476   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
477   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
478   t    = a->solve_work;
479   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
480 
481   /* solve U^T * D * y = b by forward substitution */
482   tp = t;
483   for (k=0; k<mbs; k++) { /* t <- perm(b) */
484     idx   = 6*r[k];
485     tp[0] = b[idx];
486     tp[1] = b[idx+1];
487     tp[2] = b[idx+2];
488     tp[3] = b[idx+3];
489     tp[4] = b[idx+4];
490     tp[5] = b[idx+5];
491     tp   += 6;
492   }
493 
494   for (k=0; k<mbs; k++) {
495     v  = aa + 36*ai[k];
496     vj = aj + ai[k];
497     tp = t + k*6;
498     x0 =tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4]; x5=tp[5];
499     nz = ai[k+1] - ai[k];
500     tp = t + (*vj)*6;
501     while (nz--) {
502       tp[0] +=  v[0]*x0 +  v[1]*x1 +  v[2]*x2 + v[3]*x3 + v[4]*x4 + v[5]*x5;
503       tp[1] +=  v[6]*x0 +  v[7]*x1 +  v[8]*x2 + v[9]*x3+ v[10]*x4+ v[11]*x5;
504       tp[2] += v[12]*x0 + v[13]*x1 + v[14]*x2+ v[15]*x3+ v[16]*x4+ v[17]*x5;
505       tp[3] += v[18]*x0 + v[19]*x1 + v[20]*x2+ v[21]*x3+ v[22]*x4+ v[23]*x5;
506       tp[4] += v[24]*x0 + v[25]*x1 + v[26]*x2+ v[27]*x3+ v[28]*x4+ v[29]*x5;
507       tp[5] += v[30]*x0 + v[31]*x1 + v[32]*x2+ v[33]*x3+ v[34]*x4+ v[35]*x5;
508       vj++;
509       tp = t + (*vj)*6;
510       v += 36;
511     }
512 
513     /* xk = inv(Dk)*(Dk*xk) */
514     d     = aa+k*36;       /* ptr to inv(Dk) */
515     tp    = t + k*6;
516     tp[0] = d[0]*x0 + d[6]*x1 + d[12]*x2 + d[18]*x3 + d[24]*x4 + d[30]*x5;
517     tp[1] = d[1]*x0 + d[7]*x1 + d[13]*x2 + d[19]*x3 + d[25]*x4 + d[31]*x5;
518     tp[2] = d[2]*x0 + d[8]*x1 + d[14]*x2 + d[20]*x3 + d[26]*x4 + d[32]*x5;
519     tp[3] = d[3]*x0 + d[9]*x1 + d[15]*x2 + d[21]*x3 + d[27]*x4 + d[33]*x5;
520     tp[4] = d[4]*x0+ d[10]*x1 + d[16]*x2 + d[22]*x3 + d[28]*x4 + d[34]*x5;
521     tp[5] = d[5]*x0+ d[11]*x1 + d[17]*x2 + d[23]*x3 + d[29]*x4 + d[35]*x5;
522   }
523 
524   /* solve U*x = y by back substitution */
525   for (k=mbs-1; k>=0; k--) {
526     v  = aa + 36*ai[k];
527     vj = aj + ai[k];
528     tp = t + k*6;
529     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4]; x5=tp[5]; /* xk */
530     nz = ai[k+1] - ai[k];
531 
532     tp = t + (*vj)*6;
533     while (nz--) {
534       /* xk += U(k,:)*x(:) */
535       x0 += v[0]*tp[0] + v[6]*tp[1] + v[12]*tp[2] + v[18]*tp[3] + v[24]*tp[4] + v[30]*tp[5];
536       x1 += v[1]*tp[0] + v[7]*tp[1] + v[13]*tp[2] + v[19]*tp[3] + v[25]*tp[4] + v[31]*tp[5];
537       x2 += v[2]*tp[0] + v[8]*tp[1] + v[14]*tp[2] + v[20]*tp[3] + v[26]*tp[4] + v[32]*tp[5];
538       x3 += v[3]*tp[0] + v[9]*tp[1] + v[15]*tp[2] + v[21]*tp[3] + v[27]*tp[4] + v[33]*tp[5];
539       x4 += v[4]*tp[0]+ v[10]*tp[1] + v[16]*tp[2] + v[22]*tp[3] + v[28]*tp[4] + v[34]*tp[5];
540       x5 += v[5]*tp[0]+ v[11]*tp[1] + v[17]*tp[2] + v[23]*tp[3] + v[29]*tp[4] + v[35]*tp[5];
541       vj++;
542       tp = t + (*vj)*6;
543       v += 36;
544     }
545     tp       = t + k*6;
546     tp[0]    = x0; tp[1]=x1; tp[2]=x2; tp[3]=x3; tp[4]=x4; tp[5]=x5;
547     idx      = 6*r[k];
548     x[idx]   = x0;
549     x[idx+1] = x1;
550     x[idx+2] = x2;
551     x[idx+3] = x3;
552     x[idx+4] = x4;
553     x[idx+5] = x5;
554   }
555 
556   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
557   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
558   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
559   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
560   PetscFunctionReturn(0);
561 }
562 
563 PetscErrorCode MatForwardSolve_SeqSBAIJ_6_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
564 {
565   const MatScalar *v,*d;
566   PetscScalar     *xp,x0,x1,x2,x3,x4,x5;
567   PetscInt        nz,k;
568   const PetscInt  *vj;
569 
570   PetscFunctionBegin;
571   for (k=0; k<mbs; k++) {
572     v  = aa + 36*ai[k];
573     xp = x + k*6;
574     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4]; x5=xp[5]; /* Dk*xk = k-th block of x */
575     nz = ai[k+1] - ai[k];
576     vj = aj + ai[k];
577     xp = x + (*vj)*6;
578     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
579     PetscPrefetchBlock(v+36*nz,36*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
580     while (nz--) {
581       /* x(:) += U(k,:)^T*(Dk*xk) */
582       xp[0] +=  v[0]*x0 +  v[1]*x1 +  v[2]*x2 + v[3]*x3 + v[4]*x4 + v[5]*x5;
583       xp[1] +=  v[6]*x0 +  v[7]*x1 +  v[8]*x2 + v[9]*x3+ v[10]*x4+ v[11]*x5;
584       xp[2] += v[12]*x0 + v[13]*x1 + v[14]*x2+ v[15]*x3+ v[16]*x4+ v[17]*x5;
585       xp[3] += v[18]*x0 + v[19]*x1 + v[20]*x2+ v[21]*x3+ v[22]*x4+ v[23]*x5;
586       xp[4] += v[24]*x0 + v[25]*x1 + v[26]*x2+ v[27]*x3+ v[28]*x4+ v[29]*x5;
587       xp[5] += v[30]*x0 + v[31]*x1 + v[32]*x2+ v[33]*x3+ v[34]*x4+ v[35]*x5;
588       vj++;
589       xp = x + (*vj)*6;
590       v += 36;
591     }
592     /* xk = inv(Dk)*(Dk*xk) */
593     d     = aa+k*36;       /* ptr to inv(Dk) */
594     xp    = x + k*6;
595     xp[0] = d[0]*x0 + d[6]*x1 + d[12]*x2 + d[18]*x3 + d[24]*x4 + d[30]*x5;
596     xp[1] = d[1]*x0 + d[7]*x1 + d[13]*x2 + d[19]*x3 + d[25]*x4 + d[31]*x5;
597     xp[2] = d[2]*x0 + d[8]*x1 + d[14]*x2 + d[20]*x3 + d[26]*x4 + d[32]*x5;
598     xp[3] = d[3]*x0 + d[9]*x1 + d[15]*x2 + d[21]*x3 + d[27]*x4 + d[33]*x5;
599     xp[4] = d[4]*x0+ d[10]*x1 + d[16]*x2 + d[22]*x3 + d[28]*x4 + d[34]*x5;
600     xp[5] = d[5]*x0+ d[11]*x1 + d[17]*x2 + d[23]*x3 + d[29]*x4 + d[35]*x5;
601   }
602   PetscFunctionReturn(0);
603 }
604 PetscErrorCode MatBackwardSolve_SeqSBAIJ_6_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
605 {
606   const MatScalar   *v;
607   PetscScalar       *xp,x0,x1,x2,x3,x4,x5;
608   PetscInt          nz,k;
609   const PetscInt    *vj;
610 
611   PetscFunctionBegin;
612   for (k=mbs-1; k>=0; k--) {
613     v  = aa + 36*ai[k];
614     xp = x + k*6;
615     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4]; x5=xp[5]; /* xk */
616     nz = ai[k+1] - ai[k];
617     vj = aj + ai[k];
618     xp = x + (*vj)*6;
619     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
620     PetscPrefetchBlock(v-36*nz,36*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
621     while (nz--) {
622       /* xk += U(k,:)*x(:) */
623       x0 += v[0]*xp[0] + v[6]*xp[1] + v[12]*xp[2] + v[18]*xp[3] + v[24]*xp[4] + v[30]*xp[5];
624       x1 += v[1]*xp[0] + v[7]*xp[1] + v[13]*xp[2] + v[19]*xp[3] + v[25]*xp[4] + v[31]*xp[5];
625       x2 += v[2]*xp[0] + v[8]*xp[1] + v[14]*xp[2] + v[20]*xp[3] + v[26]*xp[4] + v[32]*xp[5];
626       x3 += v[3]*xp[0] + v[9]*xp[1] + v[15]*xp[2] + v[21]*xp[3] + v[27]*xp[4] + v[33]*xp[5];
627       x4 += v[4]*xp[0]+ v[10]*xp[1] + v[16]*xp[2] + v[22]*xp[3] + v[28]*xp[4] + v[34]*xp[5];
628       x5 += v[5]*xp[0]+ v[11]*xp[1] + v[17]*xp[2] + v[23]*xp[3] + v[29]*xp[4] + v[35]*xp[5];
629       vj++;
630       v += 36; xp = x + (*vj)*6;
631     }
632     xp   = x + k*6;
633     xp[0]=x0; xp[1]=x1; xp[2]=x2; xp[3]=x3; xp[4]=x4; xp[5]=x5;
634   }
635   PetscFunctionReturn(0);
636 }
637 
638 PetscErrorCode MatSolve_SeqSBAIJ_6_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
639 {
640   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
641   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
642   const MatScalar   *aa=a->a;
643   PetscScalar       *x;
644   const PetscScalar *b;
645   PetscErrorCode    ierr;
646 
647   PetscFunctionBegin;
648   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
649   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
650 
651   /* solve U^T * D * y = b by forward substitution */
652   ierr = PetscArraycpy(x,b,6*mbs);CHKERRQ(ierr); /* x <- b */
653   ierr = MatForwardSolve_SeqSBAIJ_6_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
654 
655   /* solve U*x = y by back substitution */
656   ierr = MatBackwardSolve_SeqSBAIJ_6_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
657 
658   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
659   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
660   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
661   PetscFunctionReturn(0);
662 }
663 
664 PetscErrorCode MatForwardSolve_SeqSBAIJ_6_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
665 {
666   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
667   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
668   const MatScalar   *aa=a->a;
669   PetscScalar       *x;
670   const PetscScalar *b;
671   PetscErrorCode    ierr;
672 
673   PetscFunctionBegin;
674   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
675   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
676   ierr = PetscArraycpy(x,b,6*mbs);CHKERRQ(ierr); /* x <- b */
677   ierr = MatForwardSolve_SeqSBAIJ_6_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
678   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
679   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
680   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
681   PetscFunctionReturn(0);
682 }
683 
684 PetscErrorCode MatBackwardSolve_SeqSBAIJ_6_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
685 {
686   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
687   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
688   const MatScalar   *aa=a->a;
689   PetscScalar       *x;
690   const PetscScalar *b;
691   PetscErrorCode    ierr;
692 
693   PetscFunctionBegin;
694   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
695   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
696   ierr = PetscArraycpy(x,b,6*mbs);CHKERRQ(ierr); /* x <- b */
697   ierr = MatBackwardSolve_SeqSBAIJ_6_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
698   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
699   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
700   ierr = PetscLogFlops(2.0*a->bs2*(a->nz - mbs));CHKERRQ(ierr);
701   PetscFunctionReturn(0);
702 }
703 
704 PetscErrorCode MatSolve_SeqSBAIJ_5_inplace(Mat A,Vec bb,Vec xx)
705 {
706   Mat_SeqSBAIJ      *a=(Mat_SeqSBAIJ*)A->data;
707   IS                isrow=a->row;
708   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j;
709   PetscErrorCode    ierr;
710   const PetscInt    *r,*vj;
711   PetscInt          nz,k,idx;
712   const MatScalar   *aa=a->a,*v,*diag;
713   PetscScalar       *x,x0,x1,x2,x3,x4,*t,*tp;
714   const PetscScalar *b;
715 
716   PetscFunctionBegin;
717   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
718   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
719   t    = a->solve_work;
720   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
721 
722   /* solve U^T * D * y = b by forward substitution */
723   tp = t;
724   for (k=0; k<mbs; k++) { /* t <- perm(b) */
725     idx   = 5*r[k];
726     tp[0] = b[idx];
727     tp[1] = b[idx+1];
728     tp[2] = b[idx+2];
729     tp[3] = b[idx+3];
730     tp[4] = b[idx+4];
731     tp   += 5;
732   }
733 
734   for (k=0; k<mbs; k++) {
735     v  = aa + 25*ai[k];
736     vj = aj + ai[k];
737     tp = t + k*5;
738     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4];
739     nz = ai[k+1] - ai[k];
740 
741     tp = t + (*vj)*5;
742     while (nz--) {
743       tp[0] +=  v[0]*x0 + v[1]*x1 + v[2]*x2 + v[3]*x3 + v[4]*x4;
744       tp[1] +=  v[5]*x0 + v[6]*x1 + v[7]*x2 + v[8]*x3 + v[9]*x4;
745       tp[2] += v[10]*x0+ v[11]*x1+ v[12]*x2+ v[13]*x3+ v[14]*x4;
746       tp[3] += v[15]*x0+ v[16]*x1+ v[17]*x2+ v[18]*x3+ v[19]*x4;
747       tp[4] += v[20]*x0+ v[21]*x1+ v[22]*x2+ v[23]*x3+ v[24]*x4;
748       vj++;
749       tp = t + (*vj)*5;
750       v += 25;
751     }
752 
753     /* xk = inv(Dk)*(Dk*xk) */
754     diag  = aa+k*25;          /* ptr to inv(Dk) */
755     tp    = t + k*5;
756     tp[0] = diag[0]*x0 + diag[5]*x1 + diag[10]*x2 + diag[15]*x3 + diag[20]*x4;
757     tp[1] = diag[1]*x0 + diag[6]*x1 + diag[11]*x2 + diag[16]*x3 + diag[21]*x4;
758     tp[2] = diag[2]*x0 + diag[7]*x1 + diag[12]*x2 + diag[17]*x3 + diag[22]*x4;
759     tp[3] = diag[3]*x0 + diag[8]*x1 + diag[13]*x2 + diag[18]*x3 + diag[23]*x4;
760     tp[4] = diag[4]*x0 + diag[9]*x1 + diag[14]*x2 + diag[19]*x3 + diag[24]*x4;
761   }
762 
763   /* solve U*x = y by back substitution */
764   for (k=mbs-1; k>=0; k--) {
765     v  = aa + 25*ai[k];
766     vj = aj + ai[k];
767     tp = t + k*5;
768     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; x4=tp[4]; /* xk */
769     nz = ai[k+1] - ai[k];
770 
771     tp = t + (*vj)*5;
772     while (nz--) {
773       /* xk += U(k,:)*x(:) */
774       x0 += v[0]*tp[0] + v[5]*tp[1] + v[10]*tp[2] + v[15]*tp[3] + v[20]*tp[4];
775       x1 += v[1]*tp[0] + v[6]*tp[1] + v[11]*tp[2] + v[16]*tp[3] + v[21]*tp[4];
776       x2 += v[2]*tp[0] + v[7]*tp[1] + v[12]*tp[2] + v[17]*tp[3] + v[22]*tp[4];
777       x3 += v[3]*tp[0] + v[8]*tp[1] + v[13]*tp[2] + v[18]*tp[3] + v[23]*tp[4];
778       x4 += v[4]*tp[0] + v[9]*tp[1] + v[14]*tp[2] + v[19]*tp[3] + v[24]*tp[4];
779       vj++;
780       tp = t + (*vj)*5;
781       v += 25;
782     }
783     tp       = t + k*5;
784     tp[0]    = x0; tp[1]=x1; tp[2]=x2; tp[3]=x3; tp[4]=x4;
785     idx      = 5*r[k];
786     x[idx]   = x0;
787     x[idx+1] = x1;
788     x[idx+2] = x2;
789     x[idx+3] = x3;
790     x[idx+4] = x4;
791   }
792 
793   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
794   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
795   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
796   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
797   PetscFunctionReturn(0);
798 }
799 
800 PetscErrorCode MatForwardSolve_SeqSBAIJ_5_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
801 {
802   const MatScalar *v,*diag;
803   PetscScalar     *xp,x0,x1,x2,x3,x4;
804   PetscInt        nz,k;
805   const PetscInt  *vj;
806 
807   PetscFunctionBegin;
808   for (k=0; k<mbs; k++) {
809     v  = aa + 25*ai[k];
810     xp = x + k*5;
811     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4];/* Dk*xk = k-th block of x */
812     nz = ai[k+1] - ai[k];
813     vj = aj + ai[k];
814     xp = x + (*vj)*5;
815     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
816     PetscPrefetchBlock(v+25*nz,25*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
817     while (nz--) {
818       /* x(:) += U(k,:)^T*(Dk*xk) */
819       xp[0] +=  v[0]*x0 +  v[1]*x1 +  v[2]*x2 + v[3]*x3 + v[4]*x4;
820       xp[1] +=  v[5]*x0 +  v[6]*x1 +  v[7]*x2 + v[8]*x3 + v[9]*x4;
821       xp[2] += v[10]*x0 + v[11]*x1 + v[12]*x2+ v[13]*x3+ v[14]*x4;
822       xp[3] += v[15]*x0 + v[16]*x1 + v[17]*x2+ v[18]*x3+ v[19]*x4;
823       xp[4] += v[20]*x0 + v[21]*x1 + v[22]*x2+ v[23]*x3+ v[24]*x4;
824       vj++;
825       xp = x + (*vj)*5;
826       v += 25;
827     }
828     /* xk = inv(Dk)*(Dk*xk) */
829     diag  = aa+k*25;         /* ptr to inv(Dk) */
830     xp    = x + k*5;
831     xp[0] = diag[0]*x0 + diag[5]*x1 + diag[10]*x2 + diag[15]*x3 + diag[20]*x4;
832     xp[1] = diag[1]*x0 + diag[6]*x1 + diag[11]*x2 + diag[16]*x3 + diag[21]*x4;
833     xp[2] = diag[2]*x0 + diag[7]*x1 + diag[12]*x2 + diag[17]*x3 + diag[22]*x4;
834     xp[3] = diag[3]*x0 + diag[8]*x1 + diag[13]*x2 + diag[18]*x3 + diag[23]*x4;
835     xp[4] = diag[4]*x0 + diag[9]*x1 + diag[14]*x2 + diag[19]*x3 + diag[24]*x4;
836   }
837   PetscFunctionReturn(0);
838 }
839 
840 PetscErrorCode MatBackwardSolve_SeqSBAIJ_5_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
841 {
842   const MatScalar *v;
843   PetscScalar     *xp,x0,x1,x2,x3,x4;
844   PetscInt        nz,k;
845   const PetscInt  *vj;
846 
847   PetscFunctionBegin;
848   for (k=mbs-1; k>=0; k--) {
849     v  = aa + 25*ai[k];
850     xp = x + k*5;
851     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; x4=xp[4]; /* xk */
852     nz = ai[k+1] - ai[k];
853     vj = aj + ai[k];
854     xp = x + (*vj)*5;
855     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
856     PetscPrefetchBlock(v-25*nz,25*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
857     while (nz--) {
858       /* xk += U(k,:)*x(:) */
859       x0 += v[0]*xp[0] + v[5]*xp[1] + v[10]*xp[2] + v[15]*xp[3] + v[20]*xp[4];
860       x1 += v[1]*xp[0] + v[6]*xp[1] + v[11]*xp[2] + v[16]*xp[3] + v[21]*xp[4];
861       x2 += v[2]*xp[0] + v[7]*xp[1] + v[12]*xp[2] + v[17]*xp[3] + v[22]*xp[4];
862       x3 += v[3]*xp[0] + v[8]*xp[1] + v[13]*xp[2] + v[18]*xp[3] + v[23]*xp[4];
863       x4 += v[4]*xp[0] + v[9]*xp[1] + v[14]*xp[2] + v[19]*xp[3] + v[24]*xp[4];
864       vj++;
865       v += 25; xp = x + (*vj)*5;
866     }
867     xp   = x + k*5;
868     xp[0]=x0; xp[1]=x1; xp[2]=x2; xp[3]=x3; xp[4]=x4;
869   }
870   PetscFunctionReturn(0);
871 }
872 
873 PetscErrorCode MatSolve_SeqSBAIJ_5_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
874 {
875   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
876   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
877   const MatScalar   *aa=a->a;
878   PetscScalar       *x;
879   const PetscScalar *b;
880   PetscErrorCode    ierr;
881 
882   PetscFunctionBegin;
883   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
884   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
885 
886   /* solve U^T * D * y = b by forward substitution */
887   ierr = PetscArraycpy(x,b,5*mbs);CHKERRQ(ierr); /* x <- b */
888   ierr = MatForwardSolve_SeqSBAIJ_5_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
889 
890   /* solve U*x = y by back substitution */
891   ierr = MatBackwardSolve_SeqSBAIJ_5_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
892 
893   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
894   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
895   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
896   PetscFunctionReturn(0);
897 }
898 
899 PetscErrorCode MatForwardSolve_SeqSBAIJ_5_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
900 {
901   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
902   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
903   const MatScalar   *aa=a->a;
904   PetscScalar       *x;
905   const PetscScalar *b;
906   PetscErrorCode    ierr;
907 
908   PetscFunctionBegin;
909   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
910   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
911   ierr = PetscArraycpy(x,b,5*mbs);CHKERRQ(ierr); /* x <- b */
912   ierr = MatForwardSolve_SeqSBAIJ_5_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
913   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
914   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
915   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
916   PetscFunctionReturn(0);
917 }
918 
919 PetscErrorCode MatBackwardSolve_SeqSBAIJ_5_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
920 {
921   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
922   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
923   const MatScalar   *aa=a->a;
924   PetscScalar       *x;
925   const PetscScalar *b;
926   PetscErrorCode    ierr;
927 
928   PetscFunctionBegin;
929   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
930   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
931   ierr = PetscArraycpy(x,b,5*mbs);CHKERRQ(ierr);
932   ierr = MatBackwardSolve_SeqSBAIJ_5_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
933   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
934   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
935   ierr = PetscLogFlops(2.0*a->bs2*(a->nz-mbs));CHKERRQ(ierr);
936   PetscFunctionReturn(0);
937 }
938 
939 PetscErrorCode MatSolve_SeqSBAIJ_4_inplace(Mat A,Vec bb,Vec xx)
940 {
941   Mat_SeqSBAIJ      *a   =(Mat_SeqSBAIJ*)A->data;
942   IS                isrow=a->row;
943   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j;
944   PetscErrorCode    ierr;
945   const PetscInt    *r,*vj;
946   PetscInt          nz,k,idx;
947   const MatScalar   *aa=a->a,*v,*diag;
948   PetscScalar       *x,x0,x1,x2,x3,*t,*tp;
949   const PetscScalar *b;
950 
951   PetscFunctionBegin;
952   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
953   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
954   t    = a->solve_work;
955   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
956 
957   /* solve U^T * D * y = b by forward substitution */
958   tp = t;
959   for (k=0; k<mbs; k++) { /* t <- perm(b) */
960     idx   = 4*r[k];
961     tp[0] = b[idx];
962     tp[1] = b[idx+1];
963     tp[2] = b[idx+2];
964     tp[3] = b[idx+3];
965     tp   += 4;
966   }
967 
968   for (k=0; k<mbs; k++) {
969     v  = aa + 16*ai[k];
970     vj = aj + ai[k];
971     tp = t + k*4;
972     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3];
973     nz = ai[k+1] - ai[k];
974 
975     tp = t + (*vj)*4;
976     while (nz--) {
977       tp[0] += v[0]*x0 + v[1]*x1 + v[2]*x2 + v[3]*x3;
978       tp[1] += v[4]*x0 + v[5]*x1 + v[6]*x2 + v[7]*x3;
979       tp[2] += v[8]*x0 + v[9]*x1 + v[10]*x2+ v[11]*x3;
980       tp[3] += v[12]*x0+ v[13]*x1+ v[14]*x2+ v[15]*x3;
981       vj++;
982       tp = t + (*vj)*4;
983       v += 16;
984     }
985 
986     /* xk = inv(Dk)*(Dk*xk) */
987     diag  = aa+k*16;          /* ptr to inv(Dk) */
988     tp    = t + k*4;
989     tp[0] = diag[0]*x0 + diag[4]*x1 + diag[8]*x2 + diag[12]*x3;
990     tp[1] = diag[1]*x0 + diag[5]*x1 + diag[9]*x2 + diag[13]*x3;
991     tp[2] = diag[2]*x0 + diag[6]*x1 + diag[10]*x2+ diag[14]*x3;
992     tp[3] = diag[3]*x0 + diag[7]*x1 + diag[11]*x2+ diag[15]*x3;
993   }
994 
995   /* solve U*x = y by back substitution */
996   for (k=mbs-1; k>=0; k--) {
997     v  = aa + 16*ai[k];
998     vj = aj + ai[k];
999     tp = t + k*4;
1000     x0 = tp[0]; x1=tp[1]; x2=tp[2]; x3=tp[3]; /* xk */
1001     nz = ai[k+1] - ai[k];
1002 
1003     tp = t + (*vj)*4;
1004     while (nz--) {
1005       /* xk += U(k,:)*x(:) */
1006       x0 += v[0]*tp[0] + v[4]*tp[1] + v[8]*tp[2] + v[12]*tp[3];
1007       x1 += v[1]*tp[0] + v[5]*tp[1] + v[9]*tp[2] + v[13]*tp[3];
1008       x2 += v[2]*tp[0] + v[6]*tp[1]+ v[10]*tp[2] + v[14]*tp[3];
1009       x3 += v[3]*tp[0] + v[7]*tp[1]+ v[11]*tp[2] + v[15]*tp[3];
1010       vj++;
1011       tp = t + (*vj)*4;
1012       v += 16;
1013     }
1014     tp       = t + k*4;
1015     tp[0]    =x0; tp[1]=x1; tp[2]=x2; tp[3]=x3;
1016     idx      = 4*r[k];
1017     x[idx]   = x0;
1018     x[idx+1] = x1;
1019     x[idx+2] = x2;
1020     x[idx+3] = x3;
1021   }
1022 
1023   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
1024   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1025   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1026   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1027   PetscFunctionReturn(0);
1028 }
1029 
1030 PetscErrorCode MatForwardSolve_SeqSBAIJ_4_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1031 {
1032   const MatScalar *v,*diag;
1033   PetscScalar     *xp,x0,x1,x2,x3;
1034   PetscInt        nz,k;
1035   const PetscInt  *vj;
1036 
1037   PetscFunctionBegin;
1038   for (k=0; k<mbs; k++) {
1039     v  = aa + 16*ai[k];
1040     xp = x + k*4;
1041     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; /* Dk*xk = k-th block of x */
1042     nz = ai[k+1] - ai[k];
1043     vj = aj + ai[k];
1044     xp = x + (*vj)*4;
1045     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
1046     PetscPrefetchBlock(v+16*nz,16*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1047     while (nz--) {
1048       /* x(:) += U(k,:)^T*(Dk*xk) */
1049       xp[0] += v[0]*x0 + v[1]*x1 + v[2]*x2 + v[3]*x3;
1050       xp[1] += v[4]*x0 + v[5]*x1 + v[6]*x2 + v[7]*x3;
1051       xp[2] += v[8]*x0 + v[9]*x1 + v[10]*x2+ v[11]*x3;
1052       xp[3] += v[12]*x0+ v[13]*x1+ v[14]*x2+ v[15]*x3;
1053       vj++;
1054       xp = x + (*vj)*4;
1055       v += 16;
1056     }
1057     /* xk = inv(Dk)*(Dk*xk) */
1058     diag  = aa+k*16;         /* ptr to inv(Dk) */
1059     xp    = x + k*4;
1060     xp[0] = diag[0]*x0 + diag[4]*x1 + diag[8]*x2 + diag[12]*x3;
1061     xp[1] = diag[1]*x0 + diag[5]*x1 + diag[9]*x2 + diag[13]*x3;
1062     xp[2] = diag[2]*x0 + diag[6]*x1 + diag[10]*x2+ diag[14]*x3;
1063     xp[3] = diag[3]*x0 + diag[7]*x1 + diag[11]*x2+ diag[15]*x3;
1064   }
1065   PetscFunctionReturn(0);
1066 }
1067 
1068 PetscErrorCode MatBackwardSolve_SeqSBAIJ_4_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1069 {
1070   const MatScalar *v;
1071   PetscScalar     *xp,x0,x1,x2,x3;
1072   PetscInt        nz,k;
1073   const PetscInt  *vj;
1074 
1075   PetscFunctionBegin;
1076   for (k=mbs-1; k>=0; k--) {
1077     v  = aa + 16*ai[k];
1078     xp = x + k*4;
1079     x0 = xp[0]; x1=xp[1]; x2=xp[2]; x3=xp[3]; /* xk */
1080     nz = ai[k+1] - ai[k];
1081     vj = aj + ai[k];
1082     xp = x + (*vj)*4;
1083     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);      /* Indices for the next row (assumes same size as this one) */
1084     PetscPrefetchBlock(v-16*nz,16*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1085     while (nz--) {
1086       /* xk += U(k,:)*x(:) */
1087       x0 += v[0]*xp[0] + v[4]*xp[1] + v[8]*xp[2] + v[12]*xp[3];
1088       x1 += v[1]*xp[0] + v[5]*xp[1] + v[9]*xp[2] + v[13]*xp[3];
1089       x2 += v[2]*xp[0] + v[6]*xp[1]+ v[10]*xp[2] + v[14]*xp[3];
1090       x3 += v[3]*xp[0] + v[7]*xp[1]+ v[11]*xp[2] + v[15]*xp[3];
1091       vj++;
1092       v += 16; xp = x + (*vj)*4;
1093     }
1094     xp    = x + k*4;
1095     xp[0] = x0; xp[1] = x1; xp[2] = x2; xp[3] = x3;
1096   }
1097   PetscFunctionReturn(0);
1098 }
1099 
1100 PetscErrorCode MatSolve_SeqSBAIJ_4_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1101 {
1102   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1103   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1104   const MatScalar   *aa=a->a;
1105   PetscScalar       *x;
1106   const PetscScalar *b;
1107   PetscErrorCode    ierr;
1108 
1109   PetscFunctionBegin;
1110   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1111   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1112 
1113   /* solve U^T * D * y = b by forward substitution */
1114   ierr = PetscArraycpy(x,b,4*mbs);CHKERRQ(ierr); /* x <- b */
1115   ierr = MatForwardSolve_SeqSBAIJ_4_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1116 
1117   /* solve U*x = y by back substitution */
1118   ierr = MatBackwardSolve_SeqSBAIJ_4_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1119   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1120   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1121   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1122   PetscFunctionReturn(0);
1123 }
1124 
1125 PetscErrorCode MatForwardSolve_SeqSBAIJ_4_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1126 {
1127   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1128   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1129   const MatScalar   *aa=a->a;
1130   PetscScalar       *x;
1131   const PetscScalar *b;
1132   PetscErrorCode    ierr;
1133 
1134   PetscFunctionBegin;
1135   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1136   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1137   ierr = PetscArraycpy(x,b,4*mbs);CHKERRQ(ierr); /* x <- b */
1138   ierr = MatForwardSolve_SeqSBAIJ_4_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1139   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1140   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1141   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
1142   PetscFunctionReturn(0);
1143 }
1144 
1145 PetscErrorCode MatBackwardSolve_SeqSBAIJ_4_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1146 {
1147   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1148   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1149   const MatScalar   *aa=a->a;
1150   PetscScalar       *x;
1151   const PetscScalar *b;
1152   PetscErrorCode    ierr;
1153 
1154   PetscFunctionBegin;
1155   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1156   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1157   ierr = PetscArraycpy(x,b,4*mbs);CHKERRQ(ierr);
1158   ierr = MatBackwardSolve_SeqSBAIJ_4_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1159   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1160   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1161   ierr = PetscLogFlops(2.0*a->bs2*(a->nz-mbs));CHKERRQ(ierr);
1162   PetscFunctionReturn(0);
1163 }
1164 
1165 PetscErrorCode MatSolve_SeqSBAIJ_3_inplace(Mat A,Vec bb,Vec xx)
1166 {
1167   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1168   IS                isrow=a->row;
1169   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j;
1170   PetscErrorCode    ierr;
1171   const PetscInt    *r;
1172   PetscInt          nz,k,idx;
1173   const PetscInt    *vj;
1174   const MatScalar   *aa=a->a,*v,*diag;
1175   PetscScalar       *x,x0,x1,x2,*t,*tp;
1176   const PetscScalar *b;
1177 
1178   PetscFunctionBegin;
1179   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1180   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1181   t    = a->solve_work;
1182   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
1183 
1184   /* solve U^T * D * y = b by forward substitution */
1185   tp = t;
1186   for (k=0; k<mbs; k++) { /* t <- perm(b) */
1187     idx   = 3*r[k];
1188     tp[0] = b[idx];
1189     tp[1] = b[idx+1];
1190     tp[2] = b[idx+2];
1191     tp   += 3;
1192   }
1193 
1194   for (k=0; k<mbs; k++) {
1195     v  = aa + 9*ai[k];
1196     vj = aj + ai[k];
1197     tp = t + k*3;
1198     x0 = tp[0]; x1 = tp[1]; x2 = tp[2];
1199     nz = ai[k+1] - ai[k];
1200 
1201     tp = t + (*vj)*3;
1202     while (nz--) {
1203       tp[0] += v[0]*x0 + v[1]*x1 + v[2]*x2;
1204       tp[1] += v[3]*x0 + v[4]*x1 + v[5]*x2;
1205       tp[2] += v[6]*x0 + v[7]*x1 + v[8]*x2;
1206       vj++;
1207       tp = t + (*vj)*3;
1208       v += 9;
1209     }
1210 
1211     /* xk = inv(Dk)*(Dk*xk) */
1212     diag  = aa+k*9;          /* ptr to inv(Dk) */
1213     tp    = t + k*3;
1214     tp[0] = diag[0]*x0 + diag[3]*x1 + diag[6]*x2;
1215     tp[1] = diag[1]*x0 + diag[4]*x1 + diag[7]*x2;
1216     tp[2] = diag[2]*x0 + diag[5]*x1 + diag[8]*x2;
1217   }
1218 
1219   /* solve U*x = y by back substitution */
1220   for (k=mbs-1; k>=0; k--) {
1221     v  = aa + 9*ai[k];
1222     vj = aj + ai[k];
1223     tp = t + k*3;
1224     x0 = tp[0]; x1 = tp[1]; x2 = tp[2];  /* xk */
1225     nz = ai[k+1] - ai[k];
1226 
1227     tp = t + (*vj)*3;
1228     while (nz--) {
1229       /* xk += U(k,:)*x(:) */
1230       x0 += v[0]*tp[0] + v[3]*tp[1] + v[6]*tp[2];
1231       x1 += v[1]*tp[0] + v[4]*tp[1] + v[7]*tp[2];
1232       x2 += v[2]*tp[0] + v[5]*tp[1] + v[8]*tp[2];
1233       vj++;
1234       tp = t + (*vj)*3;
1235       v += 9;
1236     }
1237     tp       = t + k*3;
1238     tp[0]    = x0; tp[1] = x1; tp[2] = x2;
1239     idx      = 3*r[k];
1240     x[idx]   = x0;
1241     x[idx+1] = x1;
1242     x[idx+2] = x2;
1243   }
1244 
1245   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
1246   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1247   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1248   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1249   PetscFunctionReturn(0);
1250 }
1251 
1252 PetscErrorCode MatForwardSolve_SeqSBAIJ_3_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1253 {
1254   const MatScalar *v,*diag;
1255   PetscScalar     *xp,x0,x1,x2;
1256   PetscInt        nz,k;
1257   const PetscInt  *vj;
1258 
1259   PetscFunctionBegin;
1260   for (k=0; k<mbs; k++) {
1261     v  = aa + 9*ai[k];
1262     xp = x + k*3;
1263     x0 = xp[0]; x1 = xp[1]; x2 = xp[2]; /* Dk*xk = k-th block of x */
1264     nz = ai[k+1] - ai[k];
1265     vj = aj + ai[k];
1266     xp = x + (*vj)*3;
1267     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);    /* Indices for the next row (assumes same size as this one) */
1268     PetscPrefetchBlock(v+9*nz,9*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1269     while (nz--) {
1270       /* x(:) += U(k,:)^T*(Dk*xk) */
1271       xp[0] += v[0]*x0 + v[1]*x1 + v[2]*x2;
1272       xp[1] += v[3]*x0 + v[4]*x1 + v[5]*x2;
1273       xp[2] += v[6]*x0 + v[7]*x1 + v[8]*x2;
1274       vj++;
1275       xp = x + (*vj)*3;
1276       v += 9;
1277     }
1278     /* xk = inv(Dk)*(Dk*xk) */
1279     diag  = aa+k*9;         /* ptr to inv(Dk) */
1280     xp    = x + k*3;
1281     xp[0] = diag[0]*x0 + diag[3]*x1 + diag[6]*x2;
1282     xp[1] = diag[1]*x0 + diag[4]*x1 + diag[7]*x2;
1283     xp[2] = diag[2]*x0 + diag[5]*x1 + diag[8]*x2;
1284   }
1285   PetscFunctionReturn(0);
1286 }
1287 
1288 PetscErrorCode MatBackwardSolve_SeqSBAIJ_3_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1289 {
1290   const MatScalar *v;
1291   PetscScalar     *xp,x0,x1,x2;
1292   PetscInt        nz,k;
1293   const PetscInt  *vj;
1294 
1295   PetscFunctionBegin;
1296   for (k=mbs-1; k>=0; k--) {
1297     v  = aa + 9*ai[k];
1298     xp = x + k*3;
1299     x0 = xp[0]; x1 = xp[1]; x2 = xp[2];  /* xk */
1300     nz = ai[k+1] - ai[k];
1301     vj = aj + ai[k];
1302     xp = x + (*vj)*3;
1303     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);    /* Indices for the next row (assumes same size as this one) */
1304     PetscPrefetchBlock(v-9*nz,9*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1305     while (nz--) {
1306       /* xk += U(k,:)*x(:) */
1307       x0 += v[0]*xp[0] + v[3]*xp[1] + v[6]*xp[2];
1308       x1 += v[1]*xp[0] + v[4]*xp[1] + v[7]*xp[2];
1309       x2 += v[2]*xp[0] + v[5]*xp[1] + v[8]*xp[2];
1310       vj++;
1311       v += 9; xp = x + (*vj)*3;
1312     }
1313     xp    = x + k*3;
1314     xp[0] = x0; xp[1] = x1; xp[2] = x2;
1315   }
1316   PetscFunctionReturn(0);
1317 }
1318 
1319 PetscErrorCode MatSolve_SeqSBAIJ_3_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1320 {
1321   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1322   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1323   const MatScalar   *aa=a->a;
1324   PetscScalar       *x;
1325   const PetscScalar *b;
1326   PetscErrorCode    ierr;
1327 
1328   PetscFunctionBegin;
1329   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1330   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1331 
1332   /* solve U^T * D * y = b by forward substitution */
1333   ierr = PetscArraycpy(x,b,3*mbs);CHKERRQ(ierr);
1334   ierr = MatForwardSolve_SeqSBAIJ_3_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1335 
1336   /* solve U*x = y by back substitution */
1337   ierr = MatBackwardSolve_SeqSBAIJ_3_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1338 
1339   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1340   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1341   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1342   PetscFunctionReturn(0);
1343 }
1344 
1345 PetscErrorCode MatForwardSolve_SeqSBAIJ_3_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1346 {
1347   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1348   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1349   const MatScalar   *aa=a->a;
1350   PetscScalar       *x;
1351   const PetscScalar *b;
1352   PetscErrorCode    ierr;
1353 
1354   PetscFunctionBegin;
1355   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1356   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1357   ierr = PetscArraycpy(x,b,3*mbs);CHKERRQ(ierr);
1358   ierr = MatForwardSolve_SeqSBAIJ_3_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1359   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1360   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1361   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
1362   PetscFunctionReturn(0);
1363 }
1364 
1365 PetscErrorCode MatBackwardSolve_SeqSBAIJ_3_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1366 {
1367   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1368   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1369   const MatScalar   *aa=a->a;
1370   PetscScalar       *x;
1371   const PetscScalar *b;
1372   PetscErrorCode    ierr;
1373 
1374   PetscFunctionBegin;
1375   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1376   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1377   ierr = PetscArraycpy(x,b,3*mbs);CHKERRQ(ierr);
1378   ierr = MatBackwardSolve_SeqSBAIJ_3_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1379   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1380   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1381   ierr = PetscLogFlops(2.0*a->bs2*(a->nz-mbs));CHKERRQ(ierr);
1382   PetscFunctionReturn(0);
1383 }
1384 
1385 PetscErrorCode MatSolve_SeqSBAIJ_2_inplace(Mat A,Vec bb,Vec xx)
1386 {
1387   Mat_SeqSBAIJ      *a   =(Mat_SeqSBAIJ*)A->data;
1388   IS                isrow=a->row;
1389   const PetscInt    mbs  =a->mbs,*ai=a->i,*aj=a->j;
1390   PetscErrorCode    ierr;
1391   const PetscInt    *r,*vj;
1392   PetscInt          nz,k,k2,idx;
1393   const MatScalar   *aa=a->a,*v,*diag;
1394   PetscScalar       *x,x0,x1,*t;
1395   const PetscScalar *b;
1396 
1397   PetscFunctionBegin;
1398   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1399   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1400   t    = a->solve_work;
1401   ierr = ISGetIndices(isrow,&r);CHKERRQ(ierr);
1402 
1403   /* solve U^T * D * y = perm(b) by forward substitution */
1404   for (k=0; k<mbs; k++) {  /* t <- perm(b) */
1405     idx      = 2*r[k];
1406     t[k*2]   = b[idx];
1407     t[k*2+1] = b[idx+1];
1408   }
1409   for (k=0; k<mbs; k++) {
1410     v  = aa + 4*ai[k];
1411     vj = aj + ai[k];
1412     k2 = k*2;
1413     x0 = t[k2]; x1 = t[k2+1];
1414     nz = ai[k+1] - ai[k];
1415     while (nz--) {
1416       t[(*vj)*2]   += v[0]*x0 + v[1]*x1;
1417       t[(*vj)*2+1] += v[2]*x0 + v[3]*x1;
1418       vj++; v      += 4;
1419     }
1420     diag    = aa+k*4; /* ptr to inv(Dk) */
1421     t[k2]   = diag[0]*x0 + diag[2]*x1;
1422     t[k2+1] = diag[1]*x0 + diag[3]*x1;
1423   }
1424 
1425   /* solve U*x = y by back substitution */
1426   for (k=mbs-1; k>=0; k--) {
1427     v  = aa + 4*ai[k];
1428     vj = aj + ai[k];
1429     k2 = k*2;
1430     x0 = t[k2]; x1 = t[k2+1];
1431     nz = ai[k+1] - ai[k];
1432     while (nz--) {
1433       x0 += v[0]*t[(*vj)*2] + v[2]*t[(*vj)*2+1];
1434       x1 += v[1]*t[(*vj)*2] + v[3]*t[(*vj)*2+1];
1435       vj++;
1436       v += 4;
1437     }
1438     t[k2]    = x0;
1439     t[k2+1]  = x1;
1440     idx      = 2*r[k];
1441     x[idx]   = x0;
1442     x[idx+1] = x1;
1443   }
1444 
1445   ierr = ISRestoreIndices(isrow,&r);CHKERRQ(ierr);
1446   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1447   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1448   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1449   PetscFunctionReturn(0);
1450 }
1451 
1452 PetscErrorCode MatForwardSolve_SeqSBAIJ_2_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1453 {
1454   const MatScalar *v,*diag;
1455   PetscScalar     x0,x1;
1456   PetscInt        nz,k,k2;
1457   const PetscInt  *vj;
1458 
1459   PetscFunctionBegin;
1460   for (k=0; k<mbs; k++) {
1461     v  = aa + 4*ai[k];
1462     vj = aj + ai[k];
1463     k2 = k*2;
1464     x0 = x[k2]; x1 = x[k2+1];  /* Dk*xk = k-th block of x */
1465     nz = ai[k+1] - ai[k];
1466     PetscPrefetchBlock(vj+nz,nz,0,PETSC_PREFETCH_HINT_NTA);    /* Indices for the next row (assumes same size as this one) */
1467     PetscPrefetchBlock(v+4*nz,4*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1468     while (nz--) {
1469       /* x(:) += U(k,:)^T*(Dk*xk) */
1470       x[(*vj)*2]   += v[0]*x0 + v[1]*x1;
1471       x[(*vj)*2+1] += v[2]*x0 + v[3]*x1;
1472       vj++; v      += 4;
1473     }
1474     /* xk = inv(Dk)*(Dk*xk) */
1475     diag    = aa+k*4;       /* ptr to inv(Dk) */
1476     x[k2]   = diag[0]*x0 + diag[2]*x1;
1477     x[k2+1] = diag[1]*x0 + diag[3]*x1;
1478   }
1479   PetscFunctionReturn(0);
1480 }
1481 
1482 PetscErrorCode MatBackwardSolve_SeqSBAIJ_2_NaturalOrdering(const PetscInt *ai,const PetscInt *aj,const MatScalar *aa,PetscInt mbs,PetscScalar *x)
1483 {
1484   const MatScalar *v;
1485   PetscScalar     x0,x1;
1486   PetscInt        nz,k,k2;
1487   const PetscInt  *vj;
1488 
1489   PetscFunctionBegin;
1490   for (k=mbs-1; k>=0; k--) {
1491     v  = aa + 4*ai[k];
1492     vj = aj + ai[k];
1493     k2 = k*2;
1494     x0 = x[k2]; x1 = x[k2+1];  /* xk */
1495     nz = ai[k+1] - ai[k];
1496     PetscPrefetchBlock(vj-nz,nz,0,PETSC_PREFETCH_HINT_NTA);    /* Indices for the next row (assumes same size as this one) */
1497     PetscPrefetchBlock(v-4*nz,4*nz,0,PETSC_PREFETCH_HINT_NTA); /* Entries for the next row */
1498     while (nz--) {
1499       /* xk += U(k,:)*x(:) */
1500       x0 += v[0]*x[(*vj)*2] + v[2]*x[(*vj)*2+1];
1501       x1 += v[1]*x[(*vj)*2] + v[3]*x[(*vj)*2+1];
1502       vj++;
1503       v += 4;
1504     }
1505     x[k2]   = x0;
1506     x[k2+1] = x1;
1507   }
1508   PetscFunctionReturn(0);
1509 }
1510 
1511 PetscErrorCode MatSolve_SeqSBAIJ_2_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1512 {
1513   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1514   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1515   const MatScalar   *aa=a->a;
1516   PetscScalar       *x;
1517   const PetscScalar *b;
1518   PetscErrorCode    ierr;
1519 
1520   PetscFunctionBegin;
1521   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1522   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1523 
1524   /* solve U^T * D * y = b by forward substitution */
1525   ierr = PetscArraycpy(x,b,2*mbs);CHKERRQ(ierr);
1526   ierr = MatForwardSolve_SeqSBAIJ_2_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1527 
1528   /* solve U*x = y by back substitution */
1529   ierr = MatBackwardSolve_SeqSBAIJ_2_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1530 
1531   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1532   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1533   ierr = PetscLogFlops(4.0*a->bs2*a->nz - (A->rmap->bs+2.0*a->bs2)*mbs);CHKERRQ(ierr);
1534   PetscFunctionReturn(0);
1535 }
1536 
1537 PetscErrorCode MatForwardSolve_SeqSBAIJ_2_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1538 {
1539   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1540   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1541   const MatScalar   *aa=a->a;
1542   PetscScalar       *x;
1543   const PetscScalar *b;
1544   PetscErrorCode    ierr;
1545 
1546   PetscFunctionBegin;
1547   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1548   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1549   ierr = PetscArraycpy(x,b,2*mbs);CHKERRQ(ierr);
1550   ierr = MatForwardSolve_SeqSBAIJ_2_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1551   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1552   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1553   ierr = PetscLogFlops(2.0*a->bs2*a->nz - A->rmap->bs*mbs);CHKERRQ(ierr);
1554   PetscFunctionReturn(0);
1555 }
1556 
1557 PetscErrorCode MatBackwardSolve_SeqSBAIJ_2_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
1558 {
1559   Mat_SeqSBAIJ      *a =(Mat_SeqSBAIJ*)A->data;
1560   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j;
1561   const MatScalar   *aa=a->a;
1562   PetscScalar       *x;
1563   const PetscScalar *b;
1564   PetscErrorCode    ierr;
1565 
1566   PetscFunctionBegin;
1567   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1568   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1569   ierr = PetscArraycpy(x,b,2*mbs);CHKERRQ(ierr);
1570   ierr = MatBackwardSolve_SeqSBAIJ_2_NaturalOrdering(ai,aj,aa,mbs,x);CHKERRQ(ierr);
1571   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1572   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1573   ierr = PetscLogFlops(2.0*a->bs2*(a->nz - mbs));CHKERRQ(ierr);
1574   PetscFunctionReturn(0);
1575 }
1576 
1577 PetscErrorCode MatSolve_SeqSBAIJ_1(Mat A,Vec bb,Vec xx)
1578 {
1579   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1580   IS                isrow=a->row;
1581   PetscErrorCode    ierr;
1582   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj,*adiag=a->diag;
1583   const MatScalar   *aa=a->a,*v;
1584   const PetscScalar *b;
1585   PetscScalar       *x,xk,*t;
1586   PetscInt          nz,k,j;
1587 
1588   PetscFunctionBegin;
1589   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1590   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1591   t    = a->solve_work;
1592   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1593 
1594   /* solve U^T*D*y = perm(b) by forward substitution */
1595   for (k=0; k<mbs; k++) t[k] = b[rp[k]];
1596   for (k=0; k<mbs; k++) {
1597     v  = aa + ai[k];
1598     vj = aj + ai[k];
1599     xk = t[k];
1600     nz = ai[k+1] - ai[k] - 1;
1601     for (j=0; j<nz; j++) t[vj[j]] += v[j]*xk;
1602     t[k] = xk*v[nz];   /* v[nz] = 1/D(k) */
1603   }
1604 
1605   /* solve U*perm(x) = y by back substitution */
1606   for (k=mbs-1; k>=0; k--) {
1607     v  = aa + adiag[k] - 1;
1608     vj = aj + adiag[k] - 1;
1609     nz = ai[k+1] - ai[k] - 1;
1610     for (j=0; j<nz; j++) t[k] += v[-j]*t[vj[-j]];
1611     x[rp[k]] = t[k];
1612   }
1613 
1614   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1615   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1616   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1617   ierr = PetscLogFlops(4.0*a->nz - 3.0*mbs);CHKERRQ(ierr);
1618   PetscFunctionReturn(0);
1619 }
1620 
1621 PetscErrorCode MatSolve_SeqSBAIJ_1_inplace(Mat A,Vec bb,Vec xx)
1622 {
1623   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1624   IS                isrow=a->row;
1625   PetscErrorCode    ierr;
1626   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj;
1627   const MatScalar   *aa=a->a,*v;
1628   PetscScalar       *x,xk,*t;
1629   const PetscScalar *b;
1630   PetscInt          nz,k;
1631 
1632   PetscFunctionBegin;
1633   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1634   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1635   t    = a->solve_work;
1636   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1637 
1638   /* solve U^T*D*y = perm(b) by forward substitution */
1639   for (k=0; k<mbs; k++) t[k] = b[rp[k]];
1640   for (k=0; k<mbs; k++) {
1641     v  = aa + ai[k] + 1;
1642     vj = aj + ai[k] + 1;
1643     xk = t[k];
1644     nz = ai[k+1] - ai[k] - 1;
1645     while (nz--) t[*vj++] += (*v++) * xk;
1646     t[k] = xk*aa[ai[k]];  /* aa[k] = 1/D(k) */
1647   }
1648 
1649   /* solve U*perm(x) = y by back substitution */
1650   for (k=mbs-1; k>=0; k--) {
1651     v  = aa + ai[k] + 1;
1652     vj = aj + ai[k] + 1;
1653     nz = ai[k+1] - ai[k] - 1;
1654     while (nz--) t[k] += (*v++) * t[*vj++];
1655     x[rp[k]] = t[k];
1656   }
1657 
1658   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1659   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1660   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1661   ierr = PetscLogFlops(4.0*a->nz - 3*mbs);CHKERRQ(ierr);
1662   PetscFunctionReturn(0);
1663 }
1664 
1665 PetscErrorCode MatForwardSolve_SeqSBAIJ_1(Mat A,Vec bb,Vec xx)
1666 {
1667   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1668   IS                isrow=a->row;
1669   PetscErrorCode    ierr;
1670   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj,*adiag=a->diag;
1671   const MatScalar   *aa=a->a,*v;
1672   PetscReal         diagk;
1673   PetscScalar       *x,xk;
1674   const PetscScalar *b;
1675   PetscInt          nz,k;
1676 
1677   PetscFunctionBegin;
1678   /* solve U^T*D^(1/2)*x = perm(b) by forward substitution */
1679   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1680   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1681   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1682 
1683   for (k=0; k<mbs; k++) x[k] = b[rp[k]];
1684   for (k=0; k<mbs; k++) {
1685     v  = aa + ai[k];
1686     vj = aj + ai[k];
1687     xk = x[k];
1688     nz = ai[k+1] - ai[k] - 1;
1689     while (nz--) x[*vj++] += (*v++) * xk;
1690 
1691     diagk = PetscRealPart(aa[adiag[k]]); /* note: aa[diag[k]] = 1/D(k) */
1692     if (PetscImaginaryPart(aa[adiag[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
1693     x[k] = xk*PetscSqrtReal(diagk);
1694   }
1695   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1696   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1697   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1698   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
1699   PetscFunctionReturn(0);
1700 }
1701 
1702 PetscErrorCode MatForwardSolve_SeqSBAIJ_1_inplace(Mat A,Vec bb,Vec xx)
1703 {
1704   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1705   IS                isrow=a->row;
1706   PetscErrorCode    ierr;
1707   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj;
1708   const MatScalar   *aa=a->a,*v;
1709   PetscReal         diagk;
1710   PetscScalar       *x,xk;
1711   const PetscScalar *b;
1712   PetscInt          nz,k;
1713 
1714   PetscFunctionBegin;
1715   /* solve U^T*D^(1/2)*x = perm(b) by forward substitution */
1716   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1717   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1718   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1719 
1720   for (k=0; k<mbs; k++) x[k] = b[rp[k]];
1721   for (k=0; k<mbs; k++) {
1722     v  = aa + ai[k] + 1;
1723     vj = aj + ai[k] + 1;
1724     xk = x[k];
1725     nz = ai[k+1] - ai[k] - 1;
1726     while (nz--) x[*vj++] += (*v++) * xk;
1727 
1728     diagk = PetscRealPart(aa[ai[k]]); /* note: aa[diag[k]] = 1/D(k) */
1729     if (PetscImaginaryPart(aa[ai[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
1730     x[k] = xk*PetscSqrtReal(diagk);
1731   }
1732   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1733   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1734   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1735   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
1736   PetscFunctionReturn(0);
1737 }
1738 
1739 PetscErrorCode MatBackwardSolve_SeqSBAIJ_1(Mat A,Vec bb,Vec xx)
1740 {
1741   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1742   IS                isrow=a->row;
1743   PetscErrorCode    ierr;
1744   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj,*adiag=a->diag;
1745   const MatScalar   *aa=a->a,*v;
1746   PetscReal         diagk;
1747   PetscScalar       *x,*t;
1748   const PetscScalar *b;
1749   PetscInt          nz,k;
1750 
1751   PetscFunctionBegin;
1752   /* solve D^(1/2)*U*perm(x) = b by back substitution */
1753   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1754   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1755   t    = a->solve_work;
1756   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1757 
1758   for (k=mbs-1; k>=0; k--) {
1759     v     = aa + ai[k];
1760     vj    = aj + ai[k];
1761     diagk = PetscRealPart(aa[adiag[k]]);
1762     if (PetscImaginaryPart(aa[adiag[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
1763     t[k] = b[k] * PetscSqrtReal(diagk);
1764     nz   = ai[k+1] - ai[k] - 1;
1765     while (nz--) t[k] += (*v++) * t[*vj++];
1766     x[rp[k]] = t[k];
1767   }
1768   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1769   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1770   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1771   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
1772   PetscFunctionReturn(0);
1773 }
1774 
1775 PetscErrorCode MatBackwardSolve_SeqSBAIJ_1_inplace(Mat A,Vec bb,Vec xx)
1776 {
1777   Mat_SeqSBAIJ      *a   = (Mat_SeqSBAIJ*)A->data;
1778   IS                isrow=a->row;
1779   PetscErrorCode    ierr;
1780   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*rp,*vj;
1781   const MatScalar   *aa=a->a,*v;
1782   PetscReal         diagk;
1783   PetscScalar       *x,*t;
1784   const PetscScalar *b;
1785   PetscInt          nz,k;
1786 
1787   PetscFunctionBegin;
1788   /* solve D^(1/2)*U*perm(x) = b by back substitution */
1789   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1790   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1791   t    = a->solve_work;
1792   ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1793 
1794   for (k=mbs-1; k>=0; k--) {
1795     v     = aa + ai[k] + 1;
1796     vj    = aj + ai[k] + 1;
1797     diagk = PetscRealPart(aa[ai[k]]);
1798     if (PetscImaginaryPart(aa[ai[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
1799     t[k] = b[k] * PetscSqrtReal(diagk);
1800     nz   = ai[k+1] - ai[k] - 1;
1801     while (nz--) t[k] += (*v++) * t[*vj++];
1802     x[rp[k]] = t[k];
1803   }
1804   ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1805   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1806   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1807   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
1808   PetscFunctionReturn(0);
1809 }
1810 
1811 PetscErrorCode MatSolves_SeqSBAIJ_1(Mat A,Vecs bb,Vecs xx)
1812 {
1813   Mat_SeqSBAIJ   *a = (Mat_SeqSBAIJ*)A->data;
1814   PetscErrorCode ierr;
1815 
1816   PetscFunctionBegin;
1817   if (A->rmap->bs == 1) {
1818     ierr = MatSolve_SeqSBAIJ_1(A,bb->v,xx->v);CHKERRQ(ierr);
1819   } else {
1820     IS                isrow=a->row;
1821     const PetscInt    *vj,mbs=a->mbs,*ai=a->i,*aj=a->j,*rp;
1822     const MatScalar   *aa=a->a,*v;
1823     PetscScalar       *x,*t;
1824     const PetscScalar *b;
1825     PetscInt          nz,k,n,i,j;
1826 
1827     if (bb->n > a->solves_work_n) {
1828       ierr = PetscFree(a->solves_work);CHKERRQ(ierr);
1829       ierr = PetscMalloc1(bb->n*A->rmap->N,&a->solves_work);CHKERRQ(ierr);
1830       a->solves_work_n = bb->n;
1831     }
1832     n    = bb->n;
1833     ierr = VecGetArrayRead(bb->v,&b);CHKERRQ(ierr);
1834     ierr = VecGetArray(xx->v,&x);CHKERRQ(ierr);
1835     t    = a->solves_work;
1836 
1837     ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1838 
1839     /* solve U^T*D*y = perm(b) by forward substitution */
1840     for (k=0; k<mbs; k++) {
1841       for (i=0; i<n; i++) t[n*k+i] = b[rp[k]+i*mbs]; /* values are stored interlaced in t */
1842     }
1843     for (k=0; k<mbs; k++) {
1844       v  = aa + ai[k];
1845       vj = aj + ai[k];
1846       nz = ai[k+1] - ai[k] - 1;
1847       for (j=0; j<nz; j++) {
1848         for (i=0; i<n; i++) t[n*(*vj)+i] += (*v) * t[n*k+i];
1849         v++;vj++;
1850       }
1851       for (i=0; i<n; i++) t[n*k+i] *= aa[nz];  /* note: aa[nz] = 1/D(k) */
1852     }
1853 
1854     /* solve U*perm(x) = y by back substitution */
1855     for (k=mbs-1; k>=0; k--) {
1856       v  = aa + ai[k] - 1;
1857       vj = aj + ai[k] - 1;
1858       nz = ai[k+1] - ai[k] - 1;
1859       for (j=0; j<nz; j++) {
1860         for (i=0; i<n; i++) t[n*k+i] += (*v) * t[n*(*vj)+i];
1861         v++;vj++;
1862       }
1863       for (i=0; i<n; i++) x[rp[k]+i*mbs] = t[n*k+i];
1864     }
1865 
1866     ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1867     ierr = VecRestoreArrayRead(bb->v,&b);CHKERRQ(ierr);
1868     ierr = VecRestoreArray(xx->v,&x);CHKERRQ(ierr);
1869     ierr = PetscLogFlops(bb->n*(4.0*a->nz - 3.0*mbs));CHKERRQ(ierr);
1870   }
1871   PetscFunctionReturn(0);
1872 }
1873 
1874 PetscErrorCode MatSolves_SeqSBAIJ_1_inplace(Mat A,Vecs bb,Vecs xx)
1875 {
1876   Mat_SeqSBAIJ   *a = (Mat_SeqSBAIJ*)A->data;
1877   PetscErrorCode ierr;
1878 
1879   PetscFunctionBegin;
1880   if (A->rmap->bs == 1) {
1881     ierr = MatSolve_SeqSBAIJ_1_inplace(A,bb->v,xx->v);CHKERRQ(ierr);
1882   } else {
1883     IS                isrow=a->row;
1884     const PetscInt    *vj,mbs=a->mbs,*ai=a->i,*aj=a->j,*rp;
1885     const MatScalar   *aa=a->a,*v;
1886     PetscScalar       *x,*t;
1887     const PetscScalar *b;
1888     PetscInt          nz,k,n,i;
1889 
1890     if (bb->n > a->solves_work_n) {
1891       ierr = PetscFree(a->solves_work);CHKERRQ(ierr);
1892       ierr = PetscMalloc1(bb->n*A->rmap->N,&a->solves_work);CHKERRQ(ierr);
1893       a->solves_work_n = bb->n;
1894     }
1895     n    = bb->n;
1896     ierr = VecGetArrayRead(bb->v,&b);CHKERRQ(ierr);
1897     ierr = VecGetArray(xx->v,&x);CHKERRQ(ierr);
1898     t    = a->solves_work;
1899 
1900     ierr = ISGetIndices(isrow,&rp);CHKERRQ(ierr);
1901 
1902     /* solve U^T*D*y = perm(b) by forward substitution */
1903     for (k=0; k<mbs; k++) {
1904       for (i=0; i<n; i++) t[n*k+i] = b[rp[k]+i*mbs];  /* values are stored interlaced in t */
1905     }
1906     for (k=0; k<mbs; k++) {
1907       v  = aa + ai[k];
1908       vj = aj + ai[k];
1909       nz = ai[k+1] - ai[k];
1910       while (nz--) {
1911         for (i=0; i<n; i++) t[n*(*vj)+i] += (*v) * t[n*k+i];
1912         v++;vj++;
1913       }
1914       for (i=0; i<n; i++) t[n*k+i] *= aa[k];  /* note: aa[k] = 1/D(k) */
1915     }
1916 
1917     /* solve U*perm(x) = y by back substitution */
1918     for (k=mbs-1; k>=0; k--) {
1919       v  = aa + ai[k];
1920       vj = aj + ai[k];
1921       nz = ai[k+1] - ai[k];
1922       while (nz--) {
1923         for (i=0; i<n; i++) t[n*k+i] += (*v) * t[n*(*vj)+i];
1924         v++;vj++;
1925       }
1926       for (i=0; i<n; i++) x[rp[k]+i*mbs] = t[n*k+i];
1927     }
1928 
1929     ierr = ISRestoreIndices(isrow,&rp);CHKERRQ(ierr);
1930     ierr = VecRestoreArrayRead(bb->v,&b);CHKERRQ(ierr);
1931     ierr = VecRestoreArray(xx->v,&x);CHKERRQ(ierr);
1932     ierr = PetscLogFlops(bb->n*(4.0*a->nz - 3.0*mbs));CHKERRQ(ierr);
1933   }
1934   PetscFunctionReturn(0);
1935 }
1936 
1937 PetscErrorCode MatSolve_SeqSBAIJ_1_NaturalOrdering(Mat A,Vec bb,Vec xx)
1938 {
1939   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
1940   PetscErrorCode    ierr;
1941   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*vj,*adiag=a->diag;
1942   const MatScalar   *aa=a->a,*v;
1943   const PetscScalar *b;
1944   PetscScalar       *x,xi;
1945   PetscInt          nz,i,j;
1946 
1947   PetscFunctionBegin;
1948   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
1949   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
1950   /* solve U^T*D*y = b by forward substitution */
1951   ierr = PetscArraycpy(x,b,mbs);CHKERRQ(ierr);
1952   for (i=0; i<mbs; i++) {
1953     v  = aa + ai[i];
1954     vj = aj + ai[i];
1955     xi = x[i];
1956     nz = ai[i+1] - ai[i] - 1; /* exclude diag[i] */
1957     for (j=0; j<nz; j++) x[vj[j]] += v[j]*xi;
1958     x[i] = xi*v[nz];  /* v[nz] = aa[diag[i]] = 1/D(i) */
1959   }
1960   /* solve U*x = y by backward substitution */
1961   for (i=mbs-2; i>=0; i--) {
1962     xi = x[i];
1963     v  = aa + adiag[i] - 1; /* end of row i, excluding diag */
1964     vj = aj + adiag[i] - 1;
1965     nz = ai[i+1] - ai[i] - 1;
1966     for (j=0; j<nz; j++) xi += v[-j]*x[vj[-j]];
1967     x[i] = xi;
1968   }
1969   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
1970   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
1971   ierr = PetscLogFlops(4.0*a->nz - 3*mbs);CHKERRQ(ierr);
1972   PetscFunctionReturn(0);
1973 }
1974 
1975 PetscErrorCode MatMatSolve_SeqSBAIJ_1_NaturalOrdering(Mat A,Mat B,Mat X)
1976 {
1977   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
1978   PetscErrorCode    ierr;
1979   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*vj,*adiag=a->diag;
1980   const MatScalar   *aa=a->a,*v;
1981   const PetscScalar *b;
1982   PetscScalar       *x,xi;
1983   PetscInt          nz,i,j,neq,ldb,ldx;
1984   PetscBool         isdense;
1985 
1986   PetscFunctionBegin;
1987   if (!mbs) PetscFunctionReturn(0);
1988   ierr = PetscObjectTypeCompare((PetscObject)B,MATSEQDENSE,&isdense);CHKERRQ(ierr);
1989   if (!isdense) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"B matrix must be a SeqDense matrix");
1990   if (X != B) {
1991     ierr = PetscObjectTypeCompare((PetscObject)X,MATSEQDENSE,&isdense);CHKERRQ(ierr);
1992     if (!isdense) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"X matrix must be a SeqDense matrix");
1993   }
1994   ierr = MatDenseGetArrayRead(B,&b);CHKERRQ(ierr);
1995   ierr = MatDenseGetLDA(B,&ldb);CHKERRQ(ierr);
1996   ierr = MatDenseGetArray(X,&x);CHKERRQ(ierr);
1997   ierr = MatDenseGetLDA(X,&ldx);CHKERRQ(ierr);
1998   for (neq=0; neq<B->cmap->n; neq++) {
1999     /* solve U^T*D*y = b by forward substitution */
2000     ierr = PetscArraycpy(x,b,mbs);CHKERRQ(ierr);
2001     for (i=0; i<mbs; i++) {
2002       v  = aa + ai[i];
2003       vj = aj + ai[i];
2004       xi = x[i];
2005       nz = ai[i+1] - ai[i] - 1; /* exclude diag[i] */
2006       for (j=0; j<nz; j++) x[vj[j]] += v[j]*xi;
2007       x[i] = xi*v[nz];  /* v[nz] = aa[diag[i]] = 1/D(i) */
2008     }
2009     /* solve U*x = y by backward substitution */
2010     for (i=mbs-2; i>=0; i--) {
2011       xi = x[i];
2012       v  = aa + adiag[i] - 1; /* end of row i, excluding diag */
2013       vj = aj + adiag[i] - 1;
2014       nz = ai[i+1] - ai[i] - 1;
2015       for (j=0; j<nz; j++) xi += v[-j]*x[vj[-j]];
2016       x[i] = xi;
2017     }
2018     b += ldb;
2019     x += ldx;
2020   }
2021   ierr = MatDenseRestoreArrayRead(B,&b);CHKERRQ(ierr);
2022   ierr = MatDenseRestoreArray(X,&x);CHKERRQ(ierr);
2023   ierr = PetscLogFlops(B->cmap->n*(4.0*a->nz - 3*mbs));CHKERRQ(ierr);
2024   PetscFunctionReturn(0);
2025 }
2026 
2027 PetscErrorCode MatSolve_SeqSBAIJ_1_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
2028 {
2029   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
2030   PetscErrorCode    ierr;
2031   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*vj;
2032   const MatScalar   *aa=a->a,*v;
2033   PetscScalar       *x,xk;
2034   const PetscScalar *b;
2035   PetscInt          nz,k;
2036 
2037   PetscFunctionBegin;
2038   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
2039   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
2040 
2041   /* solve U^T*D*y = b by forward substitution */
2042   ierr = PetscArraycpy(x,b,mbs);CHKERRQ(ierr);
2043   for (k=0; k<mbs; k++) {
2044     v  = aa + ai[k] + 1;
2045     vj = aj + ai[k] + 1;
2046     xk = x[k];
2047     nz = ai[k+1] - ai[k] - 1;     /* exclude diag[k] */
2048     while (nz--) x[*vj++] += (*v++) * xk;
2049     x[k] = xk*aa[ai[k]];  /* note: aa[diag[k]] = 1/D(k) */
2050   }
2051 
2052   /* solve U*x = y by back substitution */
2053   for (k=mbs-2; k>=0; k--) {
2054     v  = aa + ai[k] + 1;
2055     vj = aj + ai[k] + 1;
2056     xk = x[k];
2057     nz = ai[k+1] - ai[k] - 1;
2058     while (nz--) {
2059       xk += (*v++) * x[*vj++];
2060     }
2061     x[k] = xk;
2062   }
2063 
2064   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
2065   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
2066   ierr = PetscLogFlops(4.0*a->nz - 3*mbs);CHKERRQ(ierr);
2067   PetscFunctionReturn(0);
2068 }
2069 
2070 PetscErrorCode MatForwardSolve_SeqSBAIJ_1_NaturalOrdering(Mat A,Vec bb,Vec xx)
2071 {
2072   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
2073   PetscErrorCode    ierr;
2074   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*adiag=a->diag,*vj;
2075   const MatScalar   *aa=a->a,*v;
2076   PetscReal         diagk;
2077   PetscScalar       *x;
2078   const PetscScalar *b;
2079   PetscInt          nz,k;
2080 
2081   PetscFunctionBegin;
2082   /* solve U^T*D^(1/2)*x = b by forward substitution */
2083   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
2084   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
2085   ierr = PetscArraycpy(x,b,mbs);CHKERRQ(ierr);
2086   for (k=0; k<mbs; k++) {
2087     v  = aa + ai[k];
2088     vj = aj + ai[k];
2089     nz = ai[k+1] - ai[k] - 1;     /* exclude diag[k] */
2090     while (nz--) x[*vj++] += (*v++) * x[k];
2091     diagk = PetscRealPart(aa[adiag[k]]); /* note: aa[adiag[k]] = 1/D(k) */
2092     if (PetscImaginaryPart(aa[adiag[k]]) || diagk < 0) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal (%g,%g) must be real and nonnegative",PetscRealPart(aa[adiag[k]]),PetscImaginaryPart(aa[adiag[k]]));
2093     x[k] *= PetscSqrtReal(diagk);
2094   }
2095   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
2096   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
2097   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
2098   PetscFunctionReturn(0);
2099 }
2100 
2101 PetscErrorCode MatForwardSolve_SeqSBAIJ_1_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
2102 {
2103   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
2104   PetscErrorCode    ierr;
2105   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*vj;
2106   const MatScalar   *aa=a->a,*v;
2107   PetscReal         diagk;
2108   PetscScalar       *x;
2109   const PetscScalar *b;
2110   PetscInt          nz,k;
2111 
2112   PetscFunctionBegin;
2113   /* solve U^T*D^(1/2)*x = b by forward substitution */
2114   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
2115   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
2116   ierr = PetscArraycpy(x,b,mbs);CHKERRQ(ierr);
2117   for (k=0; k<mbs; k++) {
2118     v  = aa + ai[k] + 1;
2119     vj = aj + ai[k] + 1;
2120     nz = ai[k+1] - ai[k] - 1;     /* exclude diag[k] */
2121     while (nz--) x[*vj++] += (*v++) * x[k];
2122     diagk = PetscRealPart(aa[ai[k]]); /* note: aa[diag[k]] = 1/D(k) */
2123     if (PetscImaginaryPart(aa[ai[k]]) || diagk < 0) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal (%g,%g) must be real and nonnegative",PetscRealPart(aa[ai[k]]),PetscImaginaryPart(aa[ai[k]]));
2124     x[k] *= PetscSqrtReal(diagk);
2125   }
2126   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
2127   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
2128   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
2129   PetscFunctionReturn(0);
2130 }
2131 
2132 PetscErrorCode MatBackwardSolve_SeqSBAIJ_1_NaturalOrdering(Mat A,Vec bb,Vec xx)
2133 {
2134   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
2135   PetscErrorCode    ierr;
2136   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*adiag=a->diag,*vj;
2137   const MatScalar   *aa=a->a,*v;
2138   PetscReal         diagk;
2139   PetscScalar       *x;
2140   const PetscScalar *b;
2141   PetscInt          nz,k;
2142 
2143   PetscFunctionBegin;
2144   /* solve D^(1/2)*U*x = b by back substitution */
2145   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
2146   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
2147 
2148   for (k=mbs-1; k>=0; k--) {
2149     v     = aa + ai[k];
2150     vj    = aj + ai[k];
2151     diagk = PetscRealPart(aa[adiag[k]]); /* note: aa[diag[k]] = 1/D(k) */
2152     if (PetscImaginaryPart(aa[adiag[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
2153     x[k] = PetscSqrtReal(diagk)*b[k];
2154     nz   = ai[k+1] - ai[k] - 1;
2155     while (nz--) x[k] += (*v++) * x[*vj++];
2156   }
2157   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
2158   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
2159   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
2160   PetscFunctionReturn(0);
2161 }
2162 
2163 PetscErrorCode MatBackwardSolve_SeqSBAIJ_1_NaturalOrdering_inplace(Mat A,Vec bb,Vec xx)
2164 {
2165   Mat_SeqSBAIJ      *a = (Mat_SeqSBAIJ*)A->data;
2166   PetscErrorCode    ierr;
2167   const PetscInt    mbs=a->mbs,*ai=a->i,*aj=a->j,*vj;
2168   const MatScalar   *aa=a->a,*v;
2169   PetscReal         diagk;
2170   PetscScalar       *x;
2171   const PetscScalar *b;
2172   PetscInt          nz,k;
2173 
2174   PetscFunctionBegin;
2175   /* solve D^(1/2)*U*x = b by back substitution */
2176   ierr = VecGetArrayRead(bb,&b);CHKERRQ(ierr);
2177   ierr = VecGetArray(xx,&x);CHKERRQ(ierr);
2178 
2179   for (k=mbs-1; k>=0; k--) {
2180     v     = aa + ai[k] + 1;
2181     vj    = aj + ai[k] + 1;
2182     diagk = PetscRealPart(aa[ai[k]]); /* note: aa[diag[k]] = 1/D(k) */
2183     if (PetscImaginaryPart(aa[ai[k]]) || diagk < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Diagonal must be real and nonnegative");
2184     x[k] = PetscSqrtReal(diagk)*b[k];
2185     nz   = ai[k+1] - ai[k] - 1;
2186     while (nz--) x[k] += (*v++) * x[*vj++];
2187   }
2188   ierr = VecRestoreArrayRead(bb,&b);CHKERRQ(ierr);
2189   ierr = VecRestoreArray(xx,&x);CHKERRQ(ierr);
2190   ierr = PetscLogFlops(2.0*a->nz - mbs);CHKERRQ(ierr);
2191   PetscFunctionReturn(0);
2192 }
2193 
2194 /* Use Modified Sparse Row storage for u and ju, see Saad pp.85 */
2195 PetscErrorCode MatICCFactorSymbolic_SeqSBAIJ_MSR(Mat B,Mat A,IS perm,const MatFactorInfo *info)
2196 {
2197   Mat_SeqSBAIJ   *a = (Mat_SeqSBAIJ*)A->data,*b;
2198   PetscErrorCode ierr;
2199   const PetscInt *rip,mbs = a->mbs,*ai,*aj;
2200   PetscInt       *jutmp,bs = A->rmap->bs,i;
2201   PetscInt       m,reallocs = 0,*levtmp;
2202   PetscInt       *prowl,*q,jmin,jmax,juidx,nzk,qm,*iu,*ju,k,j,vj,umax,maxadd;
2203   PetscInt       incrlev,*lev,shift,prow,nz;
2204   PetscReal      f = info->fill,levels = info->levels;
2205   PetscBool      perm_identity;
2206 
2207   PetscFunctionBegin;
2208   /* check whether perm is the identity mapping */
2209   ierr = ISIdentity(perm,&perm_identity);CHKERRQ(ierr);
2210 
2211   if (perm_identity) {
2212     a->permute = PETSC_FALSE;
2213     ai         = a->i; aj = a->j;
2214   } else { /*  non-trivial permutation */
2215     SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Matrix reordering is not supported for sbaij matrix. Use aij format");
2216   }
2217 
2218   /* initialization */
2219   ierr  = ISGetIndices(perm,&rip);CHKERRQ(ierr);
2220   umax  = (PetscInt)(f*ai[mbs] + 1);
2221   ierr  = PetscMalloc1(umax,&lev);CHKERRQ(ierr);
2222   umax += mbs + 1;
2223   shift = mbs + 1;
2224   ierr  = PetscMalloc1(mbs+1,&iu);CHKERRQ(ierr);
2225   ierr  = PetscMalloc1(umax,&ju);CHKERRQ(ierr);
2226   iu[0] = mbs + 1;
2227   juidx = mbs + 1;
2228   /* prowl: linked list for pivot row */
2229   ierr = PetscMalloc3(mbs,&prowl,mbs,&q,mbs,&levtmp);CHKERRQ(ierr);
2230   /* q: linked list for col index */
2231 
2232   for (i=0; i<mbs; i++) {
2233     prowl[i] = mbs;
2234     q[i]     = 0;
2235   }
2236 
2237   /* for each row k */
2238   for (k=0; k<mbs; k++) {
2239     nzk  = 0;
2240     q[k] = mbs;
2241     /* copy current row into linked list */
2242     nz = ai[rip[k]+1] - ai[rip[k]];
2243     j  = ai[rip[k]];
2244     while (nz--) {
2245       vj = rip[aj[j++]];
2246       if (vj > k) {
2247         qm = k;
2248         do {
2249           m = qm; qm = q[m];
2250         } while (qm < vj);
2251         if (qm == vj) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Duplicate entry in A\n");
2252         nzk++;
2253         q[m]       = vj;
2254         q[vj]      = qm;
2255         levtmp[vj] = 0;   /* initialize lev for nonzero element */
2256       }
2257     }
2258 
2259     /* modify nonzero structure of k-th row by computing fill-in
2260        for each row prow to be merged in */
2261     prow = k;
2262     prow = prowl[prow]; /* next pivot row (== 0 for symbolic factorization) */
2263 
2264     while (prow < k) {
2265       /* merge row prow into k-th row */
2266       jmin = iu[prow] + 1;
2267       jmax = iu[prow+1];
2268       qm   = k;
2269       for (j=jmin; j<jmax; j++) {
2270         incrlev = lev[j-shift] + 1;
2271         if (incrlev > levels) continue;
2272         vj = ju[j];
2273         do {
2274           m = qm; qm = q[m];
2275         } while (qm < vj);
2276         if (qm != vj) {      /* a fill */
2277           nzk++; q[m] = vj; q[vj] = qm; qm = vj;
2278           levtmp[vj] = incrlev;
2279         } else if (levtmp[vj] > incrlev) levtmp[vj] = incrlev;
2280       }
2281       prow = prowl[prow]; /* next pivot row */
2282     }
2283 
2284     /* add k to row list for first nonzero element in k-th row */
2285     if (nzk > 1) {
2286       i        = q[k]; /* col value of first nonzero element in k_th row of U */
2287       prowl[k] = prowl[i]; prowl[i] = k;
2288     }
2289     iu[k+1] = iu[k] + nzk;
2290 
2291     /* allocate more space to ju and lev if needed */
2292     if (iu[k+1] > umax) {
2293       /* estimate how much additional space we will need */
2294       /* use the strategy suggested by David Hysom <hysom@perch-t.icase.edu> */
2295       /* just double the memory each time */
2296       maxadd = umax;
2297       if (maxadd < nzk) maxadd = (mbs-k)*(nzk+1)/2;
2298       umax += maxadd;
2299 
2300       /* allocate a longer ju */
2301       ierr = PetscMalloc1(umax,&jutmp);CHKERRQ(ierr);
2302       ierr = PetscArraycpy(jutmp,ju,iu[k]);CHKERRQ(ierr);
2303       ierr = PetscFree(ju);CHKERRQ(ierr);
2304       ju   = jutmp;
2305 
2306       ierr      = PetscMalloc1(umax,&jutmp);CHKERRQ(ierr);
2307       ierr      = PetscArraycpy(jutmp,lev,iu[k]-shift);CHKERRQ(ierr);
2308       ierr      = PetscFree(lev);CHKERRQ(ierr);
2309       lev       = jutmp;
2310       reallocs += 2; /* count how many times we realloc */
2311     }
2312 
2313     /* save nonzero structure of k-th row in ju */
2314     i=k;
2315     while (nzk--) {
2316       i                = q[i];
2317       ju[juidx]        = i;
2318       lev[juidx-shift] = levtmp[i];
2319       juidx++;
2320     }
2321   }
2322 
2323 #if defined(PETSC_USE_INFO)
2324   if (ai[mbs] != 0) {
2325     PetscReal af = ((PetscReal)iu[mbs])/((PetscReal)ai[mbs]);
2326     ierr = PetscInfo3(A,"Reallocs %D Fill ratio:given %g needed %g\n",reallocs,(double)f,(double)af);CHKERRQ(ierr);
2327     ierr = PetscInfo1(A,"Run with -pc_factor_fill %g or use \n",(double)af);CHKERRQ(ierr);
2328     ierr = PetscInfo1(A,"PCFactorSetFill(pc,%g);\n",(double)af);CHKERRQ(ierr);
2329     ierr = PetscInfo(A,"for best performance.\n");CHKERRQ(ierr);
2330   } else {
2331     ierr = PetscInfo(A,"Empty matrix\n");CHKERRQ(ierr);
2332   }
2333 #endif
2334 
2335   ierr = ISRestoreIndices(perm,&rip);CHKERRQ(ierr);
2336   ierr = PetscFree3(prowl,q,levtmp);CHKERRQ(ierr);
2337   ierr = PetscFree(lev);CHKERRQ(ierr);
2338 
2339   /* put together the new matrix */
2340   ierr = MatSeqSBAIJSetPreallocation(B,bs,0,NULL);CHKERRQ(ierr);
2341 
2342   /* ierr = PetscLogObjectParent((PetscObject)B,(PetscObject)iperm);CHKERRQ(ierr); */
2343   b    = (Mat_SeqSBAIJ*)(B)->data;
2344   ierr = PetscFree2(b->imax,b->ilen);CHKERRQ(ierr);
2345 
2346   b->singlemalloc = PETSC_FALSE;
2347   b->free_a       = PETSC_TRUE;
2348   b->free_ij      = PETSC_TRUE;
2349   /* the next line frees the default space generated by the Create() */
2350   ierr    = PetscFree3(b->a,b->j,b->i);CHKERRQ(ierr);
2351   ierr    = PetscMalloc1((iu[mbs]+1)*a->bs2,&b->a);CHKERRQ(ierr);
2352   b->j    = ju;
2353   b->i    = iu;
2354   b->diag = NULL;
2355   b->ilen = NULL;
2356   b->imax = NULL;
2357 
2358   ierr    = ISDestroy(&b->row);CHKERRQ(ierr);
2359   ierr    = ISDestroy(&b->icol);CHKERRQ(ierr);
2360   b->row  = perm;
2361   b->icol = perm;
2362   ierr    = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2363   ierr    = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2364   ierr    = PetscMalloc1(bs*mbs+bs,&b->solve_work);CHKERRQ(ierr);
2365   /* In b structure:  Free imax, ilen, old a, old j.
2366      Allocate idnew, solve_work, new a, new j */
2367   ierr     = PetscLogObjectMemory((PetscObject)B,(iu[mbs]-mbs)*(sizeof(PetscInt)+sizeof(MatScalar)));CHKERRQ(ierr);
2368   b->maxnz = b->nz = iu[mbs];
2369 
2370   (B)->info.factor_mallocs   = reallocs;
2371   (B)->info.fill_ratio_given = f;
2372   if (ai[mbs] != 0) {
2373     (B)->info.fill_ratio_needed = ((PetscReal)iu[mbs])/((PetscReal)ai[mbs]);
2374   } else {
2375     (B)->info.fill_ratio_needed = 0.0;
2376   }
2377   ierr = MatSeqSBAIJSetNumericFactorization_inplace(B,perm_identity);CHKERRQ(ierr);
2378   PetscFunctionReturn(0);
2379 }
2380 
2381 /*
2382   See MatICCFactorSymbolic_SeqAIJ() for description of its data structure
2383 */
2384 #include <petscbt.h>
2385 #include <../src/mat/utils/freespace.h>
2386 PetscErrorCode MatICCFactorSymbolic_SeqSBAIJ(Mat fact,Mat A,IS perm,const MatFactorInfo *info)
2387 {
2388   Mat_SeqSBAIJ       *a = (Mat_SeqSBAIJ*)A->data,*b;
2389   PetscErrorCode     ierr;
2390   PetscBool          perm_identity,free_ij = PETSC_TRUE,missing;
2391   PetscInt           bs=A->rmap->bs,am=a->mbs,d,*ai=a->i,*aj= a->j;
2392   const PetscInt     *rip;
2393   PetscInt           reallocs=0,i,*ui,*udiag,*cols;
2394   PetscInt           jmin,jmax,nzk,k,j,*jl,prow,*il,nextprow;
2395   PetscInt           nlnk,*lnk,*lnk_lvl=NULL,ncols,*uj,**uj_ptr,**uj_lvl_ptr;
2396   PetscReal          fill          =info->fill,levels=info->levels;
2397   PetscFreeSpaceList free_space    =NULL,current_space=NULL;
2398   PetscFreeSpaceList free_space_lvl=NULL,current_space_lvl=NULL;
2399   PetscBT            lnkbt;
2400 
2401   PetscFunctionBegin;
2402   if (A->rmap->n != A->cmap->n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Must be square matrix, rows %D columns %D",A->rmap->n,A->cmap->n);
2403   ierr = MatMissingDiagonal(A,&missing,&d);CHKERRQ(ierr);
2404   if (missing) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"Matrix is missing diagonal entry %D",d);
2405   if (bs > 1) {
2406     ierr = MatICCFactorSymbolic_SeqSBAIJ_inplace(fact,A,perm,info);CHKERRQ(ierr);
2407     PetscFunctionReturn(0);
2408   }
2409 
2410   /* check whether perm is the identity mapping */
2411   ierr = ISIdentity(perm,&perm_identity);CHKERRQ(ierr);
2412   if (!perm_identity) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Matrix reordering is not supported for sbaij matrix. Use aij format");
2413   a->permute = PETSC_FALSE;
2414 
2415   ierr  = PetscMalloc1(am+1,&ui);CHKERRQ(ierr);
2416   ierr  = PetscMalloc1(am+1,&udiag);CHKERRQ(ierr);
2417   ui[0] = 0;
2418 
2419   /* ICC(0) without matrix ordering: simply rearrange column indices */
2420   if (!levels) {
2421     /* reuse the column pointers and row offsets for memory savings */
2422     for (i=0; i<am; i++) {
2423       ncols    = ai[i+1] - ai[i];
2424       ui[i+1]  = ui[i] + ncols;
2425       udiag[i] = ui[i+1] - 1; /* points to the last entry of U(i,:) */
2426     }
2427     ierr = PetscMalloc1(ui[am]+1,&uj);CHKERRQ(ierr);
2428     cols = uj;
2429     for (i=0; i<am; i++) {
2430       aj    = a->j + ai[i] + 1; /* 1st entry of U(i,:) without diagonal */
2431       ncols = ai[i+1] - ai[i] -1;
2432       for (j=0; j<ncols; j++) *cols++ = aj[j];
2433       *cols++ = i; /* diagonal is located as the last entry of U(i,:) */
2434     }
2435   } else { /* case: levels>0 */
2436     ierr = ISGetIndices(perm,&rip);CHKERRQ(ierr);
2437 
2438     /* initialization */
2439     /* jl: linked list for storing indices of the pivot rows
2440        il: il[i] points to the 1st nonzero entry of U(i,k:am-1) */
2441     ierr = PetscMalloc4(am,&uj_ptr,am,&uj_lvl_ptr,am,&il,am,&jl);CHKERRQ(ierr);
2442     for (i=0; i<am; i++) {
2443       jl[i] = am; il[i] = 0;
2444     }
2445 
2446     /* create and initialize a linked list for storing column indices of the active row k */
2447     nlnk = am + 1;
2448     ierr = PetscIncompleteLLCreate(am,am,nlnk,lnk,lnk_lvl,lnkbt);CHKERRQ(ierr);
2449 
2450     /* initial FreeSpace size is fill*(ai[am]+1) */
2451     ierr = PetscFreeSpaceGet(PetscRealIntMultTruncate(fill,ai[am]+1),&free_space);CHKERRQ(ierr);
2452 
2453     current_space = free_space;
2454 
2455     ierr = PetscFreeSpaceGet(PetscRealIntMultTruncate(fill,ai[am]+1),&free_space_lvl);CHKERRQ(ierr);
2456 
2457     current_space_lvl = free_space_lvl;
2458 
2459     for (k=0; k<am; k++) {  /* for each active row k */
2460       /* initialize lnk by the column indices of row k */
2461       nzk   = 0;
2462       ncols = ai[k+1] - ai[k];
2463       if (!ncols) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_CH_ZRPVT,"Empty row %D in matrix ",k);
2464       cols = aj+ai[k];
2465       ierr = PetscIncompleteLLInit(ncols,cols,am,rip,nlnk,lnk,lnk_lvl,lnkbt);CHKERRQ(ierr);
2466       nzk += nlnk;
2467 
2468       /* update lnk by computing fill-in for each pivot row to be merged in */
2469       prow = jl[k]; /* 1st pivot row */
2470 
2471       while (prow < k) {
2472         nextprow = jl[prow];
2473 
2474         /* merge prow into k-th row */
2475         jmin  = il[prow] + 1; /* index of the 2nd nzero entry in U(prow,k:am-1) */
2476         jmax  = ui[prow+1];
2477         ncols = jmax-jmin;
2478         i     = jmin - ui[prow];
2479 
2480         cols = uj_ptr[prow] + i;  /* points to the 2nd nzero entry in U(prow,k:am-1) */
2481         uj   = uj_lvl_ptr[prow] + i;  /* levels of cols */
2482         j    = *(uj - 1);
2483         ierr = PetscICCLLAddSorted(ncols,cols,levels,uj,am,nlnk,lnk,lnk_lvl,lnkbt,j);CHKERRQ(ierr);
2484         nzk += nlnk;
2485 
2486         /* update il and jl for prow */
2487         if (jmin < jmax) {
2488           il[prow] = jmin;
2489 
2490           j = *cols; jl[prow] = jl[j]; jl[j] = prow;
2491         }
2492         prow = nextprow;
2493       }
2494 
2495       /* if free space is not available, make more free space */
2496       if (current_space->local_remaining<nzk) {
2497         i    = am - k + 1; /* num of unfactored rows */
2498         i    = PetscIntMultTruncate(i,PetscMin(nzk, i-1)); /* i*nzk, i*(i-1): estimated and max additional space needed */
2499         ierr = PetscFreeSpaceGet(i,&current_space);CHKERRQ(ierr);
2500         ierr = PetscFreeSpaceGet(i,&current_space_lvl);CHKERRQ(ierr);
2501         reallocs++;
2502       }
2503 
2504       /* copy data into free_space and free_space_lvl, then initialize lnk */
2505       if (nzk == 0) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Empty row %D in ICC matrix factor",k);
2506       ierr = PetscIncompleteLLClean(am,am,nzk,lnk,lnk_lvl,current_space->array,current_space_lvl->array,lnkbt);CHKERRQ(ierr);
2507 
2508       /* add the k-th row into il and jl */
2509       if (nzk > 1) {
2510         i     = current_space->array[1]; /* col value of the first nonzero element in U(k, k+1:am-1) */
2511         jl[k] = jl[i]; jl[i] = k;
2512         il[k] = ui[k] + 1;
2513       }
2514       uj_ptr[k]     = current_space->array;
2515       uj_lvl_ptr[k] = current_space_lvl->array;
2516 
2517       current_space->array               += nzk;
2518       current_space->local_used          += nzk;
2519       current_space->local_remaining     -= nzk;
2520       current_space_lvl->array           += nzk;
2521       current_space_lvl->local_used      += nzk;
2522       current_space_lvl->local_remaining -= nzk;
2523 
2524       ui[k+1] = ui[k] + nzk;
2525     }
2526 
2527     ierr = ISRestoreIndices(perm,&rip);CHKERRQ(ierr);
2528     ierr = PetscFree4(uj_ptr,uj_lvl_ptr,il,jl);CHKERRQ(ierr);
2529 
2530     /* destroy list of free space and other temporary array(s) */
2531     ierr = PetscMalloc1(ui[am]+1,&uj);CHKERRQ(ierr);
2532     ierr = PetscFreeSpaceContiguous_Cholesky(&free_space,uj,am,ui,udiag);CHKERRQ(ierr); /* store matrix factor  */
2533     ierr = PetscIncompleteLLDestroy(lnk,lnkbt);CHKERRQ(ierr);
2534     ierr = PetscFreeSpaceDestroy(free_space_lvl);CHKERRQ(ierr);
2535 
2536   } /* end of case: levels>0 || (levels=0 && !perm_identity) */
2537 
2538   /* put together the new matrix in MATSEQSBAIJ format */
2539   ierr = MatSeqSBAIJSetPreallocation(fact,bs,MAT_SKIP_ALLOCATION,NULL);CHKERRQ(ierr);
2540 
2541   b    = (Mat_SeqSBAIJ*)(fact)->data;
2542   ierr = PetscFree2(b->imax,b->ilen);CHKERRQ(ierr);
2543 
2544   b->singlemalloc = PETSC_FALSE;
2545   b->free_a       = PETSC_TRUE;
2546   b->free_ij      = free_ij;
2547 
2548   ierr = PetscMalloc1(ui[am]+1,&b->a);CHKERRQ(ierr);
2549 
2550   b->j         = uj;
2551   b->i         = ui;
2552   b->diag      = udiag;
2553   b->free_diag = PETSC_TRUE;
2554   b->ilen      = NULL;
2555   b->imax      = NULL;
2556   b->row       = perm;
2557   b->col       = perm;
2558 
2559   ierr = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2560   ierr = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2561 
2562   b->pivotinblocks = PETSC_FALSE; /* need to get from MatFactorInfo */
2563 
2564   ierr = PetscMalloc1(am+1,&b->solve_work);CHKERRQ(ierr);
2565   ierr = PetscLogObjectMemory((PetscObject)fact,ui[am]*(sizeof(PetscInt)+sizeof(MatScalar)));CHKERRQ(ierr);
2566 
2567   b->maxnz = b->nz = ui[am];
2568 
2569   fact->info.factor_mallocs   = reallocs;
2570   fact->info.fill_ratio_given = fill;
2571   if (ai[am] != 0) {
2572     fact->info.fill_ratio_needed = ((PetscReal)ui[am])/ai[am];
2573   } else {
2574     fact->info.fill_ratio_needed = 0.0;
2575   }
2576 #if defined(PETSC_USE_INFO)
2577   if (ai[am] != 0) {
2578     PetscReal af = fact->info.fill_ratio_needed;
2579     ierr = PetscInfo3(A,"Reallocs %D Fill ratio:given %g needed %g\n",reallocs,(double)fill,(double)af);CHKERRQ(ierr);
2580     ierr = PetscInfo1(A,"Run with -pc_factor_fill %g or use \n",(double)af);CHKERRQ(ierr);
2581     ierr = PetscInfo1(A,"PCFactorSetFill(pc,%g) for best performance.\n",(double)af);CHKERRQ(ierr);
2582   } else {
2583     ierr = PetscInfo(A,"Empty matrix\n");CHKERRQ(ierr);
2584   }
2585 #endif
2586   fact->ops->choleskyfactornumeric = MatCholeskyFactorNumeric_SeqSBAIJ_1_NaturalOrdering;
2587   PetscFunctionReturn(0);
2588 }
2589 
2590 PetscErrorCode MatICCFactorSymbolic_SeqSBAIJ_inplace(Mat fact,Mat A,IS perm,const MatFactorInfo *info)
2591 {
2592   Mat_SeqSBAIJ       *a = (Mat_SeqSBAIJ*)A->data;
2593   Mat_SeqSBAIJ       *b;
2594   PetscErrorCode     ierr;
2595   PetscBool          perm_identity,free_ij = PETSC_TRUE;
2596   PetscInt           bs=A->rmap->bs,am=a->mbs;
2597   const PetscInt     *cols,*rip,*ai=a->i,*aj=a->j;
2598   PetscInt           reallocs=0,i,*ui;
2599   PetscInt           jmin,jmax,nzk,k,j,*jl,prow,*il,nextprow;
2600   PetscInt           nlnk,*lnk,*lnk_lvl=NULL,ncols,*cols_lvl,*uj,**uj_ptr,**uj_lvl_ptr;
2601   PetscReal          fill          =info->fill,levels=info->levels,ratio_needed;
2602   PetscFreeSpaceList free_space    =NULL,current_space=NULL;
2603   PetscFreeSpaceList free_space_lvl=NULL,current_space_lvl=NULL;
2604   PetscBT            lnkbt;
2605 
2606   PetscFunctionBegin;
2607   /*
2608    This code originally uses Modified Sparse Row (MSR) storage
2609    (see page 85, "Iterative Methods ..." by Saad) for the output matrix B - bad choice!
2610    Then it is rewritten so the factor B takes seqsbaij format. However the associated
2611    MatCholeskyFactorNumeric_() have not been modified for the cases of bs>1,
2612    thus the original code in MSR format is still used for these cases.
2613    The code below should replace MatICCFactorSymbolic_SeqSBAIJ_MSR() whenever
2614    MatCholeskyFactorNumeric_() is modified for using sbaij symbolic factor.
2615   */
2616   if (bs > 1) {
2617     ierr = MatICCFactorSymbolic_SeqSBAIJ_MSR(fact,A,perm,info);CHKERRQ(ierr);
2618     PetscFunctionReturn(0);
2619   }
2620 
2621   /* check whether perm is the identity mapping */
2622   ierr = ISIdentity(perm,&perm_identity);CHKERRQ(ierr);
2623   if (!perm_identity) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Matrix reordering is not supported for sbaij matrix. Use aij format");
2624   a->permute = PETSC_FALSE;
2625 
2626   /* special case that simply copies fill pattern */
2627   if (!levels) {
2628     /* reuse the column pointers and row offsets for memory savings */
2629     ui           = a->i;
2630     uj           = a->j;
2631     free_ij      = PETSC_FALSE;
2632     ratio_needed = 1.0;
2633   } else { /* case: levels>0 */
2634     ierr = ISGetIndices(perm,&rip);CHKERRQ(ierr);
2635 
2636     /* initialization */
2637     ierr  = PetscMalloc1(am+1,&ui);CHKERRQ(ierr);
2638     ui[0] = 0;
2639 
2640     /* jl: linked list for storing indices of the pivot rows
2641        il: il[i] points to the 1st nonzero entry of U(i,k:am-1) */
2642     ierr = PetscMalloc4(am,&uj_ptr,am,&uj_lvl_ptr,am,&il,am,&jl);CHKERRQ(ierr);
2643     for (i=0; i<am; i++) {
2644       jl[i] = am; il[i] = 0;
2645     }
2646 
2647     /* create and initialize a linked list for storing column indices of the active row k */
2648     nlnk = am + 1;
2649     ierr = PetscIncompleteLLCreate(am,am,nlnk,lnk,lnk_lvl,lnkbt);CHKERRQ(ierr);
2650 
2651     /* initial FreeSpace size is fill*(ai[am]+1) */
2652     ierr = PetscFreeSpaceGet(PetscRealIntMultTruncate(fill,ai[am]+1),&free_space);CHKERRQ(ierr);
2653 
2654     current_space = free_space;
2655 
2656     ierr = PetscFreeSpaceGet(PetscRealIntMultTruncate(fill,ai[am]+1),&free_space_lvl);CHKERRQ(ierr);
2657 
2658     current_space_lvl = free_space_lvl;
2659 
2660     for (k=0; k<am; k++) {  /* for each active row k */
2661       /* initialize lnk by the column indices of row rip[k] */
2662       nzk   = 0;
2663       ncols = ai[rip[k]+1] - ai[rip[k]];
2664       cols  = aj+ai[rip[k]];
2665       ierr  = PetscIncompleteLLInit(ncols,cols,am,rip,nlnk,lnk,lnk_lvl,lnkbt);CHKERRQ(ierr);
2666       nzk  += nlnk;
2667 
2668       /* update lnk by computing fill-in for each pivot row to be merged in */
2669       prow = jl[k]; /* 1st pivot row */
2670 
2671       while (prow < k) {
2672         nextprow = jl[prow];
2673 
2674         /* merge prow into k-th row */
2675         jmin     = il[prow] + 1; /* index of the 2nd nzero entry in U(prow,k:am-1) */
2676         jmax     = ui[prow+1];
2677         ncols    = jmax-jmin;
2678         i        = jmin - ui[prow];
2679         cols     = uj_ptr[prow] + i; /* points to the 2nd nzero entry in U(prow,k:am-1) */
2680         j        = *(uj_lvl_ptr[prow] + i - 1);
2681         cols_lvl = uj_lvl_ptr[prow]+i;
2682         ierr     = PetscICCLLAddSorted(ncols,cols,levels,cols_lvl,am,nlnk,lnk,lnk_lvl,lnkbt,j);CHKERRQ(ierr);
2683         nzk     += nlnk;
2684 
2685         /* update il and jl for prow */
2686         if (jmin < jmax) {
2687           il[prow] = jmin;
2688           j        = *cols;
2689           jl[prow] = jl[j];
2690           jl[j]    = prow;
2691         }
2692         prow = nextprow;
2693       }
2694 
2695       /* if free space is not available, make more free space */
2696       if (current_space->local_remaining<nzk) {
2697         i    = am - k + 1; /* num of unfactored rows */
2698         i    = PetscMin(PetscIntMultTruncate(i,nzk), PetscIntMultTruncate(i,i-1)); /* i*nzk, i*(i-1): estimated and max additional space needed */
2699         ierr = PetscFreeSpaceGet(i,&current_space);CHKERRQ(ierr);
2700         ierr = PetscFreeSpaceGet(i,&current_space_lvl);CHKERRQ(ierr);
2701         reallocs++;
2702       }
2703 
2704       /* copy data into free_space and free_space_lvl, then initialize lnk */
2705       ierr = PetscIncompleteLLClean(am,am,nzk,lnk,lnk_lvl,current_space->array,current_space_lvl->array,lnkbt);CHKERRQ(ierr);
2706 
2707       /* add the k-th row into il and jl */
2708       if (nzk-1 > 0) {
2709         i     = current_space->array[1]; /* col value of the first nonzero element in U(k, k+1:am-1) */
2710         jl[k] = jl[i]; jl[i] = k;
2711         il[k] = ui[k] + 1;
2712       }
2713       uj_ptr[k]     = current_space->array;
2714       uj_lvl_ptr[k] = current_space_lvl->array;
2715 
2716       current_space->array               += nzk;
2717       current_space->local_used          += nzk;
2718       current_space->local_remaining     -= nzk;
2719       current_space_lvl->array           += nzk;
2720       current_space_lvl->local_used      += nzk;
2721       current_space_lvl->local_remaining -= nzk;
2722 
2723       ui[k+1] = ui[k] + nzk;
2724     }
2725 
2726     ierr = ISRestoreIndices(perm,&rip);CHKERRQ(ierr);
2727     ierr = PetscFree4(uj_ptr,uj_lvl_ptr,il,jl);CHKERRQ(ierr);
2728 
2729     /* destroy list of free space and other temporary array(s) */
2730     ierr = PetscMalloc1(ui[am]+1,&uj);CHKERRQ(ierr);
2731     ierr = PetscFreeSpaceContiguous(&free_space,uj);CHKERRQ(ierr);
2732     ierr = PetscIncompleteLLDestroy(lnk,lnkbt);CHKERRQ(ierr);
2733     ierr = PetscFreeSpaceDestroy(free_space_lvl);CHKERRQ(ierr);
2734     if (ai[am] != 0) {
2735       ratio_needed = ((PetscReal)ui[am])/((PetscReal)ai[am]);
2736     } else {
2737       ratio_needed = 0.0;
2738     }
2739   } /* end of case: levels>0 || (levels=0 && !perm_identity) */
2740 
2741   /* put together the new matrix in MATSEQSBAIJ format */
2742   ierr = MatSeqSBAIJSetPreallocation(fact,bs,MAT_SKIP_ALLOCATION,NULL);CHKERRQ(ierr);
2743 
2744   b = (Mat_SeqSBAIJ*)(fact)->data;
2745 
2746   ierr = PetscFree2(b->imax,b->ilen);CHKERRQ(ierr);
2747 
2748   b->singlemalloc = PETSC_FALSE;
2749   b->free_a       = PETSC_TRUE;
2750   b->free_ij      = free_ij;
2751 
2752   ierr = PetscMalloc1(ui[am]+1,&b->a);CHKERRQ(ierr);
2753 
2754   b->j             = uj;
2755   b->i             = ui;
2756   b->diag          = NULL;
2757   b->ilen          = NULL;
2758   b->imax          = NULL;
2759   b->row           = perm;
2760   b->pivotinblocks = PETSC_FALSE; /* need to get from MatFactorInfo */
2761 
2762   ierr    = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2763   b->icol = perm;
2764   ierr    = PetscObjectReference((PetscObject)perm);CHKERRQ(ierr);
2765   ierr    = PetscMalloc1(am+1,&b->solve_work);CHKERRQ(ierr);
2766 
2767   b->maxnz = b->nz = ui[am];
2768 
2769   fact->info.factor_mallocs    = reallocs;
2770   fact->info.fill_ratio_given  = fill;
2771   fact->info.fill_ratio_needed = ratio_needed;
2772 #if defined(PETSC_USE_INFO)
2773   if (ai[am] != 0) {
2774     PetscReal af = fact->info.fill_ratio_needed;
2775     ierr = PetscInfo3(A,"Reallocs %D Fill ratio:given %g needed %g\n",reallocs,(double)fill,(double)af);CHKERRQ(ierr);
2776     ierr = PetscInfo1(A,"Run with -pc_factor_fill %g or use \n",(double)af);CHKERRQ(ierr);
2777     ierr = PetscInfo1(A,"PCFactorSetFill(pc,%g) for best performance.\n",(double)af);CHKERRQ(ierr);
2778   } else {
2779     ierr = PetscInfo(A,"Empty matrix\n");CHKERRQ(ierr);
2780   }
2781 #endif
2782   if (perm_identity) {
2783     fact->ops->choleskyfactornumeric = MatCholeskyFactorNumeric_SeqSBAIJ_1_NaturalOrdering_inplace;
2784   } else {
2785     fact->ops->choleskyfactornumeric = MatCholeskyFactorNumeric_SeqSBAIJ_1_inplace;
2786   }
2787   PetscFunctionReturn(0);
2788 }
2789