xref: /petsc/src/ts/tutorials/multirate/ex8.c (revision 607e733f3db3ee7f6f605a13295c517df8dbb9c9)
1 static const char help[] = "1D periodic Finite Volume solver in slope-limiter form with semidiscrete time stepping.\n"
2                            "  advection   - Constant coefficient scalar advection\n"
3                            "                u_t       + (a*u)_x               = 0\n"
4                            "  for this toy problem, we choose different meshsizes for different sub-domains (slow-medium-fast-medium-slow), \n"
5                            "  the meshsize ratio between two adjacient sub-domains is controlled with -hratio,\n"
6                            "  exact       - Exact Riemann solver which usually needs to perform a Newton iteration to connect\n"
7                            "                the states across shocks and rarefactions\n"
8                            "  simulation  - use reference solution which is generated by smaller time step size to be true solution,\n"
9                            "                also the reference solution should be generated by user and stored in a binary file.\n"
10                            "  characteristic - Limit the characteristic variables, this is usually preferred (default)\n"
11                            "Several initial conditions can be chosen with -initial N\n\n"
12                            "The problem size should be set with -da_grid_x M\n\n";
13 
14 #include <petscts.h>
15 #include <petscdm.h>
16 #include <petscdmda.h>
17 #include <petscdraw.h>
18 #include "finitevolume1d.h"
19 
20 static inline PetscReal RangeMod(PetscReal a, PetscReal xmin, PetscReal xmax)
21 {
22   PetscReal range = xmax - xmin;
23   return xmin + PetscFmodReal(range + PetscFmodReal(a, range), range);
24 }
25 
26 /* --------------------------------- Advection ----------------------------------- */
27 typedef struct {
28   PetscReal a; /* advective velocity */
29 } AdvectCtx;
30 
31 static PetscErrorCode PhysicsRiemann_Advect(void *vctx, PetscInt m, const PetscScalar *uL, const PetscScalar *uR, PetscScalar *flux, PetscReal *maxspeed)
32 {
33   AdvectCtx *ctx = (AdvectCtx *)vctx;
34   PetscReal  speed;
35 
36   PetscFunctionBeginUser;
37   speed     = ctx->a;
38   flux[0]   = PetscMax(0, speed) * uL[0] + PetscMin(0, speed) * uR[0];
39   *maxspeed = speed;
40   PetscFunctionReturn(PETSC_SUCCESS);
41 }
42 
43 static PetscErrorCode PhysicsCharacteristic_Advect(void *vctx, PetscInt m, const PetscScalar *u, PetscScalar *X, PetscScalar *Xi, PetscReal *speeds)
44 {
45   AdvectCtx *ctx = (AdvectCtx *)vctx;
46 
47   PetscFunctionBeginUser;
48   X[0]      = 1.;
49   Xi[0]     = 1.;
50   speeds[0] = ctx->a;
51   PetscFunctionReturn(PETSC_SUCCESS);
52 }
53 
54 static PetscErrorCode PhysicsSample_Advect(void *vctx, PetscInt initial, FVBCType bctype, PetscReal xmin, PetscReal xmax, PetscReal t, PetscReal x, PetscReal *u)
55 {
56   AdvectCtx *ctx = (AdvectCtx *)vctx;
57   PetscReal  a   = ctx->a, x0;
58 
59   PetscFunctionBeginUser;
60   switch (bctype) {
61   case FVBC_OUTFLOW:
62     x0 = x - a * t;
63     break;
64   case FVBC_PERIODIC:
65     x0 = RangeMod(x - a * t, xmin, xmax);
66     break;
67   default:
68     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_UNKNOWN_TYPE, "unknown BCType");
69   }
70   switch (initial) {
71   case 0:
72     u[0] = (x0 < 0) ? 1 : -1;
73     break;
74   case 1:
75     u[0] = (x0 < 0) ? -1 : 1;
76     break;
77   case 2:
78     u[0] = (0 < x0 && x0 < 1) ? 1 : 0;
79     break;
80   case 3:
81     u[0] = PetscSinReal(2 * PETSC_PI * x0);
82     break;
83   case 4:
84     u[0] = PetscAbs(x0);
85     break;
86   case 5:
87     u[0] = (x0 < 0 || x0 > 0.5) ? 0 : PetscSqr(PetscSinReal(2 * PETSC_PI * x0));
88     break;
89   case 6:
90     u[0] = (x0 < 0) ? 0 : ((x0 < 1) ? x0 : ((x0 < 2) ? 2 - x0 : 0));
91     break;
92   case 7:
93     u[0] = PetscPowReal(PetscSinReal(PETSC_PI * x0), 10.0);
94     break;
95   default:
96     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_UNKNOWN_TYPE, "unknown initial condition");
97   }
98   PetscFunctionReturn(PETSC_SUCCESS);
99 }
100 
101 static PetscErrorCode PhysicsCreate_Advect(FVCtx *ctx)
102 {
103   AdvectCtx *user;
104 
105   PetscFunctionBeginUser;
106   PetscCall(PetscNew(&user));
107   ctx->physics2.sample2         = PhysicsSample_Advect;
108   ctx->physics2.riemann2        = PhysicsRiemann_Advect;
109   ctx->physics2.characteristic2 = PhysicsCharacteristic_Advect;
110   ctx->physics2.destroy         = PhysicsDestroy_SimpleFree;
111   ctx->physics2.user            = user;
112   ctx->physics2.dof             = 1;
113   PetscCall(PetscStrallocpy("u", &ctx->physics2.fieldname[0]));
114   user->a = 1;
115   PetscOptionsBegin(ctx->comm, ctx->prefix, "Options for advection", "");
116   {
117     PetscCall(PetscOptionsReal("-physics_advect_a", "Speed", "", user->a, &user->a, NULL));
118   }
119   PetscOptionsEnd();
120   PetscFunctionReturn(PETSC_SUCCESS);
121 }
122 
123 PetscErrorCode FVSample_3WaySplit(FVCtx *ctx, DM da, PetscReal time, Vec U)
124 {
125   PetscScalar   *u, *uj, xj, xi;
126   PetscInt       i, j, k, dof, xs, xm, Mx;
127   const PetscInt N = 200;
128   PetscReal      hs, hm, hf;
129 
130   PetscFunctionBeginUser;
131   PetscCheck(ctx->physics2.sample2, PETSC_COMM_SELF, PETSC_ERR_SUP, "Physics has not provided a sampling function");
132   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
133   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
134   PetscCall(DMDAVecGetArray(da, U, &u));
135   PetscCall(PetscMalloc1(dof, &uj));
136 
137   hs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
138   hm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
139   hf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
140   for (i = xs; i < xs + xm; i++) {
141     if (i < ctx->sm) {
142       xi = ctx->xmin + 0.5 * hs + i * hs;
143       /* Integrate over cell i using trapezoid rule with N points. */
144       for (k = 0; k < dof; k++) u[i * dof + k] = 0;
145       for (j = 0; j < N + 1; j++) {
146         xj = xi + hs * (j - N / 2) / (PetscReal)N;
147         PetscCall((*ctx->physics2.sample2)(ctx->physics2.user, ctx->initial, ctx->bctype, ctx->xmin, ctx->xmax, time, xj, uj));
148         for (k = 0; k < dof; k++) u[i * dof + k] += ((j == 0 || j == N) ? 0.5 : 1.0) * uj[k] / N;
149       }
150     } else if (i < ctx->mf) {
151       xi = ctx->xmin + ctx->sm * hs + 0.5 * hm + (i - ctx->sm) * hm;
152       /* Integrate over cell i using trapezoid rule with N points. */
153       for (k = 0; k < dof; k++) u[i * dof + k] = 0;
154       for (j = 0; j < N + 1; j++) {
155         xj = xi + hm * (j - N / 2) / (PetscReal)N;
156         PetscCall((*ctx->physics2.sample2)(ctx->physics2.user, ctx->initial, ctx->bctype, ctx->xmin, ctx->xmax, time, xj, uj));
157         for (k = 0; k < dof; k++) u[i * dof + k] += ((j == 0 || j == N) ? 0.5 : 1.0) * uj[k] / N;
158       }
159     } else if (i < ctx->fm) {
160       xi = ctx->xmin + ctx->sm * hs + (ctx->mf - ctx->sm) * hm + 0.5 * hf + (i - ctx->mf) * hf;
161       /* Integrate over cell i using trapezoid rule with N points. */
162       for (k = 0; k < dof; k++) u[i * dof + k] = 0;
163       for (j = 0; j < N + 1; j++) {
164         xj = xi + hf * (j - N / 2) / (PetscReal)N;
165         PetscCall((*ctx->physics2.sample2)(ctx->physics2.user, ctx->initial, ctx->bctype, ctx->xmin, ctx->xmax, time, xj, uj));
166         for (k = 0; k < dof; k++) u[i * dof + k] += ((j == 0 || j == N) ? 0.5 : 1.0) * uj[k] / N;
167       }
168     } else if (i < ctx->ms) {
169       xi = ctx->xmin + ctx->sm * hs + (ctx->mf - ctx->sm) * hm + (ctx->fm - ctx->mf) * hf + 0.5 * hm + (i - ctx->fm) * hm;
170       /* Integrate over cell i using trapezoid rule with N points. */
171       for (k = 0; k < dof; k++) u[i * dof + k] = 0;
172       for (j = 0; j < N + 1; j++) {
173         xj = xi + hm * (j - N / 2) / (PetscReal)N;
174         PetscCall((*ctx->physics2.sample2)(ctx->physics2.user, ctx->initial, ctx->bctype, ctx->xmin, ctx->xmax, time, xj, uj));
175         for (k = 0; k < dof; k++) u[i * dof + k] += ((j == 0 || j == N) ? 0.5 : 1.0) * uj[k] / N;
176       }
177     } else {
178       xi = ctx->xmin + ctx->sm * hs + (ctx->mf - ctx->sm) * hm + (ctx->fm - ctx->mf) * hf + (ctx->ms - ctx->fm) * hm + 0.5 * hs + (i - ctx->ms) * hs;
179       /* Integrate over cell i using trapezoid rule with N points. */
180       for (k = 0; k < dof; k++) u[i * dof + k] = 0;
181       for (j = 0; j < N + 1; j++) {
182         xj = xi + hs * (j - N / 2) / (PetscReal)N;
183         PetscCall((*ctx->physics2.sample2)(ctx->physics2.user, ctx->initial, ctx->bctype, ctx->xmin, ctx->xmax, time, xj, uj));
184         for (k = 0; k < dof; k++) u[i * dof + k] += ((j == 0 || j == N) ? 0.5 : 1.0) * uj[k] / N;
185       }
186     }
187   }
188   PetscCall(DMDAVecRestoreArray(da, U, &u));
189   PetscCall(PetscFree(uj));
190   PetscFunctionReturn(PETSC_SUCCESS);
191 }
192 
193 static PetscErrorCode SolutionErrorNorms_3WaySplit(FVCtx *ctx, DM da, PetscReal t, Vec X, PetscReal *nrm1)
194 {
195   Vec                Y;
196   PetscInt           i, Mx;
197   const PetscScalar *ptr_X, *ptr_Y;
198   PetscReal          hs, hm, hf;
199 
200   PetscFunctionBeginUser;
201   PetscCall(VecGetSize(X, &Mx));
202   hs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
203   hm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
204   hf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
205   PetscCall(VecDuplicate(X, &Y));
206   PetscCall(FVSample_3WaySplit(ctx, da, t, Y));
207   PetscCall(VecGetArrayRead(X, &ptr_X));
208   PetscCall(VecGetArrayRead(Y, &ptr_Y));
209   for (i = 0; i < Mx; i++) {
210     if (i < ctx->sm || i > ctx->ms - 1) *nrm1 += hs * PetscAbs(ptr_X[i] - ptr_Y[i]);
211     else if (i < ctx->mf || i > ctx->fm - 1) *nrm1 += hm * PetscAbs(ptr_X[i] - ptr_Y[i]);
212     else *nrm1 += hf * PetscAbs(ptr_X[i] - ptr_Y[i]);
213   }
214   PetscCall(VecRestoreArrayRead(X, &ptr_X));
215   PetscCall(VecRestoreArrayRead(Y, &ptr_Y));
216   PetscCall(VecDestroy(&Y));
217   PetscFunctionReturn(PETSC_SUCCESS);
218 }
219 
220 PetscErrorCode FVRHSFunction_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
221 {
222   FVCtx       *ctx = (FVCtx *)vctx;
223   PetscInt     i, j, k, Mx, dof, xs, xm, sm = ctx->sm, mf = ctx->mf, fm = ctx->fm, ms = ctx->ms;
224   PetscReal    hxf, hxm, hxs, cfl_idt = 0;
225   PetscScalar *x, *f, *slope;
226   Vec          Xloc;
227   DM           da;
228 
229   PetscFunctionBeginUser;
230   PetscCall(TSGetDM(ts, &da));
231   PetscCall(DMGetLocalVector(da, &Xloc));                                 /* Xloc contains ghost points                                     */
232   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0)); /* Mx is the number of center points                              */
233   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
234   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
235   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
236   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc)); /* X is solution vector which does not contain ghost points       */
237   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
238 
239   PetscCall(VecZeroEntries(F)); /* F is the right-hand side function corresponds to center points */
240 
241   PetscCall(DMDAVecGetArray(da, Xloc, &x));
242   PetscCall(DMDAVecGetArray(da, F, &f));
243   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope)); /* contains ghost points                                           */
244 
245   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
246 
247   if (ctx->bctype == FVBC_OUTFLOW) {
248     for (i = xs - 2; i < 0; i++) {
249       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
250     }
251     for (i = Mx; i < xs + xm + 2; i++) {
252       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
253     }
254   }
255   for (i = xs - 1; i < xs + xm + 1; i++) {
256     struct _LimitInfo info;
257     PetscScalar      *cjmpL, *cjmpR;
258     /* Determine the right eigenvectors R, where A = R \Lambda R^{-1} */
259     PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
260     /* Evaluate jumps across interfaces (i-1, i) and (i, i+1), put in characteristic basis */
261     PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
262     cjmpL = &ctx->cjmpLR[0];
263     cjmpR = &ctx->cjmpLR[dof];
264     for (j = 0; j < dof; j++) {
265       PetscScalar jmpL, jmpR;
266       jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
267       jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
268       for (k = 0; k < dof; k++) {
269         cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
270         cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
271       }
272     }
273     /* Apply limiter to the left and right characteristic jumps */
274     info.m   = dof;
275     info.hxs = hxs;
276     info.hxm = hxm;
277     info.hxf = hxf;
278     (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
279     for (j = 0; j < dof; j++) {
280       PetscScalar tmp = 0;
281       for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
282       slope[i * dof + j] = tmp;
283     }
284   }
285 
286   for (i = xs; i < xs + xm + 1; i++) {
287     PetscReal    maxspeed;
288     PetscScalar *uL, *uR;
289     uL = &ctx->uLR[0];
290     uR = &ctx->uLR[dof];
291     if (i < sm || i > ms) { /* slow region */
292       for (j = 0; j < dof; j++) {
293         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
294         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
295       }
296       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
297       if (i > xs) {
298         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxs;
299       }
300       if (i < xs + xm) {
301         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxs;
302       }
303     } else if (i == sm) { /* interface between slow and medium component */
304       for (j = 0; j < dof; j++) {
305         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
306         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
307       }
308       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
309       if (i > xs) {
310         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxs;
311       }
312       if (i < xs + xm) {
313         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxm;
314       }
315     } else if (i == ms) { /* interface between medium and slow regions */
316       for (j = 0; j < dof; j++) {
317         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
318         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
319       }
320       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
321       if (i > xs) {
322         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxm;
323       }
324       if (i < xs + xm) {
325         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxs;
326       }
327     } else if (i < mf || i > fm) { /* medium region */
328       for (j = 0; j < dof; j++) {
329         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
330         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
331       }
332       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
333       if (i > xs) {
334         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxm;
335       }
336       if (i < xs + xm) {
337         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxm;
338       }
339     } else if (i == mf) { /* interface between medium and fast regions */
340       for (j = 0; j < dof; j++) {
341         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
342         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxf / 2;
343       }
344       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
345       if (i > xs) {
346         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxm;
347       }
348       if (i < xs + xm) {
349         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxf;
350       }
351     } else if (i == fm) { /* interface between fast and medium regions */
352       for (j = 0; j < dof; j++) {
353         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxf / 2;
354         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
355       }
356       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
357       if (i > xs) {
358         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxf;
359       }
360       if (i < xs + xm) {
361         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxm;
362       }
363     } else { /* fast region */
364       for (j = 0; j < dof; j++) {
365         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxf / 2;
366         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxf / 2;
367       }
368       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
369       cfl_idt = PetscMax(cfl_idt, PetscAbsScalar(maxspeed / hxs)); /* Max allowable value of 1/Delta t */
370       if (i > xs) {
371         for (j = 0; j < dof; j++) f[(i - 1) * dof + j] -= ctx->flux[j] / hxf;
372       }
373       if (i < xs + xm) {
374         for (j = 0; j < dof; j++) f[i * dof + j] += ctx->flux[j] / hxf;
375       }
376     }
377   }
378   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
379   PetscCall(DMDAVecRestoreArray(da, F, &f));
380   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
381   PetscCall(DMRestoreLocalVector(da, &Xloc));
382   PetscCallMPI(MPIU_Allreduce(&cfl_idt, &ctx->cfl_idt, 1, MPIU_SCALAR, MPIU_MAX, PetscObjectComm((PetscObject)da)));
383   if (0) {
384     /* We need to a way to inform the TS of a CFL constraint, this is a debugging fragment */
385     PetscReal dt, tnow;
386     PetscCall(TSGetTimeStep(ts, &dt));
387     PetscCall(TSGetTime(ts, &tnow));
388     if (dt > 0.5 / ctx->cfl_idt) PetscCall(PetscPrintf(ctx->comm, "Stability constraint exceeded at t=%g, dt %g > %g\n", (double)tnow, (double)dt, (double)(1 / (2 * ctx->cfl_idt))));
389   }
390   PetscFunctionReturn(PETSC_SUCCESS);
391 }
392 
393 /* --------------------------------- Finite Volume Solver for slow components ----------------------------------- */
394 PetscErrorCode FVRHSFunctionslow_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
395 {
396   FVCtx       *ctx = (FVCtx *)vctx;
397   PetscInt     i, j, k, Mx, dof, xs, xm, islow = 0, sm = ctx->sm, ms = ctx->ms, lsbwidth = ctx->lsbwidth, rsbwidth = ctx->rsbwidth;
398   PetscReal    hxs, hxm, hxf, cfl_idt = 0;
399   PetscScalar *x, *f, *slope;
400   Vec          Xloc;
401   DM           da;
402 
403   PetscFunctionBeginUser;
404   PetscCall(TSGetDM(ts, &da));
405   PetscCall(DMGetLocalVector(da, &Xloc));
406   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
407   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
408   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
409   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
410   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc));
411   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
412   PetscCall(VecZeroEntries(F));
413   PetscCall(DMDAVecGetArray(da, Xloc, &x));
414   PetscCall(VecGetArray(F, &f));
415   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope));
416   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
417 
418   if (ctx->bctype == FVBC_OUTFLOW) {
419     for (i = xs - 2; i < 0; i++) {
420       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
421     }
422     for (i = Mx; i < xs + xm + 2; i++) {
423       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
424     }
425   }
426   for (i = xs - 1; i < xs + xm + 1; i++) {
427     struct _LimitInfo info;
428     PetscScalar      *cjmpL, *cjmpR;
429     if (i < sm - lsbwidth + 1 || i > ms + rsbwidth - 2) { /* slow components and the first and last fast components */
430       /* Determine the right eigenvectors R, where A = R \Lambda R^{-1} */
431       PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
432       /* Evaluate jumps across interfaces (i-1, i) and (i, i+1), put in characteristic basis */
433       PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
434       cjmpL = &ctx->cjmpLR[0];
435       cjmpR = &ctx->cjmpLR[dof];
436       for (j = 0; j < dof; j++) {
437         PetscScalar jmpL, jmpR;
438         jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
439         jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
440         for (k = 0; k < dof; k++) {
441           cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
442           cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
443         }
444       }
445       /* Apply limiter to the left and right characteristic jumps */
446       info.m   = dof;
447       info.hxs = hxs;
448       info.hxm = hxm;
449       info.hxf = hxf;
450       (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
451       for (j = 0; j < dof; j++) {
452         PetscScalar tmp = 0;
453         for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
454         slope[i * dof + j] = tmp;
455       }
456     }
457   }
458 
459   for (i = xs; i < xs + xm + 1; i++) {
460     PetscReal    maxspeed;
461     PetscScalar *uL, *uR;
462     uL = &ctx->uLR[0];
463     uR = &ctx->uLR[dof];
464     if (i < sm - lsbwidth) { /* slow region */
465       for (j = 0; j < dof; j++) {
466         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
467         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
468       }
469       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
470       cfl_idt = PetscMax(cfl_idt, PetscAbsScalar(maxspeed / hxs)); /* Max allowable value of 1/Delta t */
471       if (i > xs) {
472         for (j = 0; j < dof; j++) f[(islow - 1) * dof + j] -= ctx->flux[j] / hxs;
473       }
474       if (i < xs + xm) {
475         for (j = 0; j < dof; j++) f[islow * dof + j] += ctx->flux[j] / hxs;
476         islow++;
477       }
478     }
479     if (i == sm - lsbwidth) { /* interface between slow and medium regions */
480       for (j = 0; j < dof; j++) {
481         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
482         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
483       }
484       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
485       if (i > xs) {
486         for (j = 0; j < dof; j++) f[(islow - 1) * dof + j] -= ctx->flux[j] / hxs;
487       }
488     }
489     if (i == ms + rsbwidth) { /* interface between medium and slow regions */
490       for (j = 0; j < dof; j++) {
491         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
492         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
493       }
494       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
495       if (i < xs + xm) {
496         for (j = 0; j < dof; j++) f[islow * dof + j] += ctx->flux[j] / hxs;
497         islow++;
498       }
499     }
500     if (i > ms + rsbwidth) { /* slow region */
501       for (j = 0; j < dof; j++) {
502         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
503         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
504       }
505       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
506       cfl_idt = PetscMax(cfl_idt, PetscAbsScalar(maxspeed / hxs)); /* Max allowable value of 1/Delta t */
507       if (i > xs) {
508         for (j = 0; j < dof; j++) f[(islow - 1) * dof + j] -= ctx->flux[j] / hxs;
509       }
510       if (i < xs + xm) {
511         for (j = 0; j < dof; j++) f[islow * dof + j] += ctx->flux[j] / hxs;
512         islow++;
513       }
514     }
515   }
516   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
517   PetscCall(VecRestoreArray(F, &f));
518   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
519   PetscCall(DMRestoreLocalVector(da, &Xloc));
520   PetscCallMPI(MPIU_Allreduce(&cfl_idt, &ctx->cfl_idt, 1, MPIU_SCALAR, MPIU_MAX, PetscObjectComm((PetscObject)da)));
521   PetscFunctionReturn(PETSC_SUCCESS);
522 }
523 
524 PetscErrorCode FVRHSFunctionslowbuffer_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
525 {
526   FVCtx       *ctx = (FVCtx *)vctx;
527   PetscInt     i, j, k, Mx, dof, xs, xm, islowbuffer = 0, sm = ctx->sm, ms = ctx->ms, lsbwidth = ctx->lsbwidth, rsbwidth = ctx->rsbwidth;
528   PetscReal    hxs, hxm, hxf;
529   PetscScalar *x, *f, *slope;
530   Vec          Xloc;
531   DM           da;
532 
533   PetscFunctionBeginUser;
534   PetscCall(TSGetDM(ts, &da));
535   PetscCall(DMGetLocalVector(da, &Xloc));
536   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
537   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
538   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
539   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
540   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc));
541   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
542   PetscCall(VecZeroEntries(F));
543   PetscCall(DMDAVecGetArray(da, Xloc, &x));
544   PetscCall(VecGetArray(F, &f));
545   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope));
546   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
547 
548   if (ctx->bctype == FVBC_OUTFLOW) {
549     for (i = xs - 2; i < 0; i++) {
550       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
551     }
552     for (i = Mx; i < xs + xm + 2; i++) {
553       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
554     }
555   }
556   for (i = xs - 1; i < xs + xm + 1; i++) {
557     struct _LimitInfo info;
558     PetscScalar      *cjmpL, *cjmpR;
559     if ((i > sm - lsbwidth - 2 && i < sm + 1) || (i > ms - 2 && i < ms + rsbwidth + 1)) {
560       /* Determine the right eigenvectors R, where A = R \Lambda R^{-1} */
561       PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
562       /* Evaluate jumps across interfaces (i-1, i) and (i, i+1), put in characteristic basis */
563       PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
564       cjmpL = &ctx->cjmpLR[0];
565       cjmpR = &ctx->cjmpLR[dof];
566       for (j = 0; j < dof; j++) {
567         PetscScalar jmpL, jmpR;
568         jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
569         jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
570         for (k = 0; k < dof; k++) {
571           cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
572           cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
573         }
574       }
575       /* Apply limiter to the left and right characteristic jumps */
576       info.m   = dof;
577       info.hxs = hxs;
578       info.hxm = hxm;
579       info.hxf = hxf;
580       (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
581       for (j = 0; j < dof; j++) {
582         PetscScalar tmp = 0;
583         for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
584         slope[i * dof + j] = tmp;
585       }
586     }
587   }
588 
589   for (i = xs; i < xs + xm + 1; i++) {
590     PetscReal    maxspeed;
591     PetscScalar *uL, *uR;
592     uL = &ctx->uLR[0];
593     uR = &ctx->uLR[dof];
594     if (i == sm - lsbwidth) {
595       for (j = 0; j < dof; j++) {
596         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
597         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
598       }
599       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
600       if (i < xs + xm) {
601         for (j = 0; j < dof; j++) f[islowbuffer * dof + j] += ctx->flux[j] / hxs;
602         islowbuffer++;
603       }
604     }
605     if (i > sm - lsbwidth && i < sm) {
606       for (j = 0; j < dof; j++) {
607         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
608         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
609       }
610       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
611       if (i > xs) {
612         for (j = 0; j < dof; j++) f[(islowbuffer - 1) * dof + j] -= ctx->flux[j] / hxs;
613       }
614       if (i < xs + xm) {
615         for (j = 0; j < dof; j++) f[islowbuffer * dof + j] += ctx->flux[j] / hxs;
616         islowbuffer++;
617       }
618     }
619     if (i == sm) { /* interface between the slow region and the medium region */
620       for (j = 0; j < dof; j++) {
621         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
622         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
623       }
624       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
625       if (i > xs) {
626         for (j = 0; j < dof; j++) f[(islowbuffer - 1) * dof + j] -= ctx->flux[j] / hxs;
627       }
628     }
629     if (i == ms) { /* interface between the medium region and the slow region */
630       for (j = 0; j < dof; j++) {
631         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
632         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
633       }
634       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
635       if (i < xs + xm) {
636         for (j = 0; j < dof; j++) f[islowbuffer * dof + j] += ctx->flux[j] / hxs;
637         islowbuffer++;
638       }
639     }
640     if (i > ms && i < ms + rsbwidth) {
641       for (j = 0; j < dof; j++) {
642         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
643         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
644       }
645       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
646       if (i > xs) {
647         for (j = 0; j < dof; j++) f[(islowbuffer - 1) * dof + j] -= ctx->flux[j] / hxs;
648       }
649       if (i < xs + xm) {
650         for (j = 0; j < dof; j++) f[islowbuffer * dof + j] += ctx->flux[j] / hxs;
651         islowbuffer++;
652       }
653     }
654     if (i == ms + rsbwidth) {
655       for (j = 0; j < dof; j++) {
656         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
657         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
658       }
659       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
660       if (i > xs) {
661         for (j = 0; j < dof; j++) f[(islowbuffer - 1) * dof + j] -= ctx->flux[j] / hxs;
662       }
663     }
664   }
665   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
666   PetscCall(VecRestoreArray(F, &f));
667   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
668   PetscCall(DMRestoreLocalVector(da, &Xloc));
669   PetscFunctionReturn(PETSC_SUCCESS);
670 }
671 
672 /* --------------------------------- Finite Volume Solver for medium components ----------------------------------- */
673 PetscErrorCode FVRHSFunctionmedium_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
674 {
675   FVCtx       *ctx = (FVCtx *)vctx;
676   PetscInt     i, j, k, Mx, dof, xs, xm, imedium = 0, sm = ctx->sm, mf = ctx->mf, fm = ctx->fm, ms = ctx->ms, lmbwidth = ctx->lmbwidth, rmbwidth = ctx->rmbwidth;
677   PetscReal    hxs, hxm, hxf;
678   PetscScalar *x, *f, *slope;
679   Vec          Xloc;
680   DM           da;
681 
682   PetscFunctionBeginUser;
683   PetscCall(TSGetDM(ts, &da));
684   PetscCall(DMGetLocalVector(da, &Xloc));
685   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
686   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
687   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
688   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
689   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc));
690   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
691   PetscCall(VecZeroEntries(F));
692   PetscCall(DMDAVecGetArray(da, Xloc, &x));
693   PetscCall(VecGetArray(F, &f));
694   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope));
695   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
696 
697   if (ctx->bctype == FVBC_OUTFLOW) {
698     for (i = xs - 2; i < 0; i++) {
699       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
700     }
701     for (i = Mx; i < xs + xm + 2; i++) {
702       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
703     }
704   }
705   for (i = xs - 1; i < xs + xm + 1; i++) {
706     struct _LimitInfo info;
707     PetscScalar      *cjmpL, *cjmpR;
708     if ((i > sm - 2 && i < mf - lmbwidth + 1) || (i > fm + rmbwidth - 2 && i < ms + 1)) { /* slow components and the first and last fast components */
709       /* Determine the right eigenvectors R, where A = R \Lambda R^{-1} */
710       PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
711       /* Evaluate jumps across interfaces (i-1, i) and (i, i+1), put in characteristic basis */
712       PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
713       cjmpL = &ctx->cjmpLR[0];
714       cjmpR = &ctx->cjmpLR[dof];
715       for (j = 0; j < dof; j++) {
716         PetscScalar jmpL, jmpR;
717         jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
718         jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
719         for (k = 0; k < dof; k++) {
720           cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
721           cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
722         }
723       }
724       /* Apply limiter to the left and right characteristic jumps */
725       info.m   = dof;
726       info.hxs = hxs;
727       info.hxm = hxm;
728       info.hxf = hxf;
729       (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
730       for (j = 0; j < dof; j++) {
731         PetscScalar tmp = 0;
732         for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
733         slope[i * dof + j] = tmp;
734       }
735     }
736   }
737 
738   for (i = xs; i < xs + xm + 1; i++) {
739     PetscReal    maxspeed;
740     PetscScalar *uL, *uR;
741     uL = &ctx->uLR[0];
742     uR = &ctx->uLR[dof];
743     if (i == sm) { /* interface between slow and medium regions */
744       for (j = 0; j < dof; j++) {
745         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxs / 2;
746         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
747       }
748       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
749       if (i < xs + xm) {
750         for (j = 0; j < dof; j++) f[imedium * dof + j] += ctx->flux[j] / hxm;
751         imedium++;
752       }
753     }
754     if (i > sm && i < mf - lmbwidth) { /* medium region */
755       for (j = 0; j < dof; j++) {
756         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
757         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
758       }
759       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
760       if (i > xs) {
761         for (j = 0; j < dof; j++) f[(imedium - 1) * dof + j] -= ctx->flux[j] / hxm;
762       }
763       if (i < xs + xm) {
764         for (j = 0; j < dof; j++) f[imedium * dof + j] += ctx->flux[j] / hxm;
765         imedium++;
766       }
767     }
768     if (i == mf - lmbwidth) { /* interface between medium and fast regions */
769       for (j = 0; j < dof; j++) {
770         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
771         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
772       }
773       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
774       if (i > xs) {
775         for (j = 0; j < dof; j++) f[(imedium - 1) * dof + j] -= ctx->flux[j] / hxm;
776       }
777     }
778     if (i == fm + rmbwidth) { /* interface between fast and medium regions */
779       for (j = 0; j < dof; j++) {
780         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
781         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
782       }
783       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
784       if (i < xs + xm) {
785         for (j = 0; j < dof; j++) f[imedium * dof + j] += ctx->flux[j] / hxm;
786         imedium++;
787       }
788     }
789     if (i > fm + rmbwidth && i < ms) { /* medium region */
790       for (j = 0; j < dof; j++) {
791         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
792         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
793       }
794       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
795       if (i > xs) {
796         for (j = 0; j < dof; j++) f[(imedium - 1) * dof + j] -= ctx->flux[j] / hxm;
797       }
798       if (i < xs + xm) {
799         for (j = 0; j < dof; j++) f[imedium * dof + j] += ctx->flux[j] / hxm;
800         imedium++;
801       }
802     }
803     if (i == ms) { /* interface between medium and slow regions */
804       for (j = 0; j < dof; j++) {
805         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
806         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxs / 2;
807       }
808       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
809       if (i > xs) {
810         for (j = 0; j < dof; j++) f[(imedium - 1) * dof + j] -= ctx->flux[j] / hxm;
811       }
812     }
813   }
814   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
815   PetscCall(VecRestoreArray(F, &f));
816   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
817   PetscCall(DMRestoreLocalVector(da, &Xloc));
818   PetscFunctionReturn(PETSC_SUCCESS);
819 }
820 
821 PetscErrorCode FVRHSFunctionmediumbuffer_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
822 {
823   FVCtx       *ctx = (FVCtx *)vctx;
824   PetscInt     i, j, k, Mx, dof, xs, xm, imediumbuffer = 0, mf = ctx->mf, fm = ctx->fm, lmbwidth = ctx->lmbwidth, rmbwidth = ctx->rmbwidth;
825   PetscReal    hxs, hxm, hxf;
826   PetscScalar *x, *f, *slope;
827   Vec          Xloc;
828   DM           da;
829 
830   PetscFunctionBeginUser;
831   PetscCall(TSGetDM(ts, &da));
832   PetscCall(DMGetLocalVector(da, &Xloc));
833   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
834   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
835   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
836   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
837   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc));
838   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
839   PetscCall(VecZeroEntries(F));
840   PetscCall(DMDAVecGetArray(da, Xloc, &x));
841   PetscCall(VecGetArray(F, &f));
842   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope));
843   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
844 
845   if (ctx->bctype == FVBC_OUTFLOW) {
846     for (i = xs - 2; i < 0; i++) {
847       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
848     }
849     for (i = Mx; i < xs + xm + 2; i++) {
850       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
851     }
852   }
853   for (i = xs - 1; i < xs + xm + 1; i++) {
854     struct _LimitInfo info;
855     PetscScalar      *cjmpL, *cjmpR;
856     if ((i > mf - lmbwidth - 2 && i < mf + 1) || (i > fm - 2 && i < fm + rmbwidth + 1)) {
857       /* Determine the right eigenvectors R, where A = R \Lambda R^{-1} */
858       PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
859       /* Evaluate jumps across interfaces (i-1, i) and (i, i+1), put in characteristic basis */
860       PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
861       cjmpL = &ctx->cjmpLR[0];
862       cjmpR = &ctx->cjmpLR[dof];
863       for (j = 0; j < dof; j++) {
864         PetscScalar jmpL, jmpR;
865         jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
866         jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
867         for (k = 0; k < dof; k++) {
868           cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
869           cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
870         }
871       }
872       /* Apply limiter to the left and right characteristic jumps */
873       info.m   = dof;
874       info.hxs = hxs;
875       info.hxm = hxm;
876       info.hxf = hxf;
877       (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
878       for (j = 0; j < dof; j++) {
879         PetscScalar tmp = 0;
880         for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
881         slope[i * dof + j] = tmp;
882       }
883     }
884   }
885 
886   for (i = xs; i < xs + xm + 1; i++) {
887     PetscReal    maxspeed;
888     PetscScalar *uL, *uR;
889     uL = &ctx->uLR[0];
890     uR = &ctx->uLR[dof];
891     if (i == mf - lmbwidth) {
892       for (j = 0; j < dof; j++) {
893         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
894         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
895       }
896       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
897       if (i < xs + xm) {
898         for (j = 0; j < dof; j++) f[imediumbuffer * dof + j] += ctx->flux[j] / hxm;
899         imediumbuffer++;
900       }
901     }
902     if (i > mf - lmbwidth && i < mf) {
903       for (j = 0; j < dof; j++) {
904         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
905         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
906       }
907       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
908       if (i > xs) {
909         for (j = 0; j < dof; j++) f[(imediumbuffer - 1) * dof + j] -= ctx->flux[j] / hxm;
910       }
911       if (i < xs + xm) {
912         for (j = 0; j < dof; j++) f[imediumbuffer * dof + j] += ctx->flux[j] / hxm;
913         imediumbuffer++;
914       }
915     }
916     if (i == mf) { /* interface between the medium region and the fast region */
917       for (j = 0; j < dof; j++) {
918         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
919         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxf / 2;
920       }
921       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
922       if (i > xs) {
923         for (j = 0; j < dof; j++) f[(imediumbuffer - 1) * dof + j] -= ctx->flux[j] / hxm;
924       }
925     }
926     if (i == fm) { /* interface between the fast region and the medium region */
927       for (j = 0; j < dof; j++) {
928         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxf / 2;
929         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
930       }
931       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
932       if (i < xs + xm) {
933         for (j = 0; j < dof; j++) f[imediumbuffer * dof + j] += ctx->flux[j] / hxm;
934         imediumbuffer++;
935       }
936     }
937     if (i > fm && i < fm + rmbwidth) {
938       for (j = 0; j < dof; j++) {
939         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
940         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
941       }
942       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
943       if (i > xs) {
944         for (j = 0; j < dof; j++) f[(imediumbuffer - 1) * dof + j] -= ctx->flux[j] / hxm;
945       }
946       if (i < xs + xm) {
947         for (j = 0; j < dof; j++) f[imediumbuffer * dof + j] += ctx->flux[j] / hxm;
948         imediumbuffer++;
949       }
950     }
951     if (i == fm + rmbwidth) {
952       for (j = 0; j < dof; j++) {
953         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
954         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
955       }
956       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
957       if (i > xs) {
958         for (j = 0; j < dof; j++) f[(imediumbuffer - 1) * dof + j] -= ctx->flux[j] / hxm;
959       }
960     }
961   }
962   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
963   PetscCall(VecRestoreArray(F, &f));
964   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
965   PetscCall(DMRestoreLocalVector(da, &Xloc));
966   PetscFunctionReturn(PETSC_SUCCESS);
967 }
968 
969 /* --------------------------------- Finite Volume Solver for fast  parts ----------------------------------- */
970 PetscErrorCode FVRHSFunctionfast_3WaySplit(TS ts, PetscReal time, Vec X, Vec F, void *vctx)
971 {
972   FVCtx       *ctx = (FVCtx *)vctx;
973   PetscInt     i, j, k, Mx, dof, xs, xm, ifast = 0, mf = ctx->mf, fm = ctx->fm;
974   PetscReal    hxs, hxm, hxf;
975   PetscScalar *x, *f, *slope;
976   Vec          Xloc;
977   DM           da;
978 
979   PetscFunctionBeginUser;
980   PetscCall(TSGetDM(ts, &da));
981   PetscCall(DMGetLocalVector(da, &Xloc));
982   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
983   hxs = (ctx->xmax - ctx->xmin) / 8.0 / ctx->sm;
984   hxm = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->mf - ctx->sm);
985   hxf = (ctx->xmax - ctx->xmin) / 4.0 / (ctx->fm - ctx->mf);
986   PetscCall(DMGlobalToLocalBegin(da, X, INSERT_VALUES, Xloc));
987   PetscCall(DMGlobalToLocalEnd(da, X, INSERT_VALUES, Xloc));
988   PetscCall(VecZeroEntries(F));
989   PetscCall(DMDAVecGetArray(da, Xloc, &x));
990   PetscCall(VecGetArray(F, &f));
991   PetscCall(DMDAGetArray(da, PETSC_TRUE, &slope));
992   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
993 
994   if (ctx->bctype == FVBC_OUTFLOW) {
995     for (i = xs - 2; i < 0; i++) {
996       for (j = 0; j < dof; j++) x[i * dof + j] = x[j];
997     }
998     for (i = Mx; i < xs + xm + 2; i++) {
999       for (j = 0; j < dof; j++) x[i * dof + j] = x[(xs + xm - 1) * dof + j];
1000     }
1001   }
1002   for (i = xs - 1; i < xs + xm + 1; i++) { /* fast components and the last slow components before fast components and the first slow component after fast components */
1003     struct _LimitInfo info;
1004     PetscScalar      *cjmpL, *cjmpR;
1005     if (i > mf - 2 && i < fm + 1) {
1006       PetscCall((*ctx->physics2.characteristic2)(ctx->physics2.user, dof, &x[i * dof], ctx->R, ctx->Rinv, ctx->speeds));
1007       PetscCall(PetscArrayzero(ctx->cjmpLR, 2 * dof));
1008       cjmpL = &ctx->cjmpLR[0];
1009       cjmpR = &ctx->cjmpLR[dof];
1010       for (j = 0; j < dof; j++) {
1011         PetscScalar jmpL, jmpR;
1012         jmpL = x[(i + 0) * dof + j] - x[(i - 1) * dof + j];
1013         jmpR = x[(i + 1) * dof + j] - x[(i + 0) * dof + j];
1014         for (k = 0; k < dof; k++) {
1015           cjmpL[k] += ctx->Rinv[k + j * dof] * jmpL;
1016           cjmpR[k] += ctx->Rinv[k + j * dof] * jmpR;
1017         }
1018       }
1019       /* Apply limiter to the left and right characteristic jumps */
1020       info.m   = dof;
1021       info.hxs = hxs;
1022       info.hxm = hxm;
1023       info.hxf = hxf;
1024       (*ctx->limit3)(&info, cjmpL, cjmpR, ctx->sm, ctx->mf, ctx->fm, ctx->ms, i, ctx->cslope);
1025       for (j = 0; j < dof; j++) {
1026         PetscScalar tmp = 0;
1027         for (k = 0; k < dof; k++) tmp += ctx->R[j + k * dof] * ctx->cslope[k];
1028         slope[i * dof + j] = tmp;
1029       }
1030     }
1031   }
1032 
1033   for (i = xs; i < xs + xm + 1; i++) {
1034     PetscReal    maxspeed;
1035     PetscScalar *uL, *uR;
1036     uL = &ctx->uLR[0];
1037     uR = &ctx->uLR[dof];
1038     if (i == mf) { /* interface between medium and fast regions */
1039       for (j = 0; j < dof; j++) {
1040         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxm / 2;
1041         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxf / 2;
1042       }
1043       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
1044       if (i < xs + xm) {
1045         for (j = 0; j < dof; j++) f[ifast * dof + j] += ctx->flux[j] / hxf;
1046         ifast++;
1047       }
1048     }
1049     if (i > mf && i < fm) { /* fast region */
1050       for (j = 0; j < dof; j++) {
1051         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxf / 2;
1052         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxf / 2;
1053       }
1054       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
1055       if (i > xs) {
1056         for (j = 0; j < dof; j++) f[(ifast - 1) * dof + j] -= ctx->flux[j] / hxf;
1057       }
1058       if (i < xs + xm) {
1059         for (j = 0; j < dof; j++) f[ifast * dof + j] += ctx->flux[j] / hxf;
1060         ifast++;
1061       }
1062     }
1063     if (i == fm) { /* interface between fast and medium regions */
1064       for (j = 0; j < dof; j++) {
1065         uL[j] = x[(i - 1) * dof + j] + slope[(i - 1) * dof + j] * hxf / 2;
1066         uR[j] = x[(i - 0) * dof + j] - slope[(i - 0) * dof + j] * hxm / 2;
1067       }
1068       PetscCall((*ctx->physics2.riemann2)(ctx->physics2.user, dof, uL, uR, ctx->flux, &maxspeed));
1069       if (i > xs) {
1070         for (j = 0; j < dof; j++) f[(ifast - 1) * dof + j] -= ctx->flux[j] / hxf;
1071       }
1072     }
1073   }
1074   PetscCall(DMDAVecRestoreArray(da, Xloc, &x));
1075   PetscCall(VecRestoreArray(F, &f));
1076   PetscCall(DMDARestoreArray(da, PETSC_TRUE, &slope));
1077   PetscCall(DMRestoreLocalVector(da, &Xloc));
1078   PetscFunctionReturn(PETSC_SUCCESS);
1079 }
1080 
1081 int main(int argc, char *argv[])
1082 {
1083   char              lname[256] = "mc", physname[256] = "advect", final_fname[256] = "solution.m";
1084   PetscFunctionList limiters = 0, physics = 0;
1085   MPI_Comm          comm;
1086   TS                ts;
1087   DM                da;
1088   Vec               X, X0, R;
1089   FVCtx             ctx;
1090   PetscInt          i, k, dof, xs, xm, Mx, draw = 0, count_slow, count_medium, count_fast, islow = 0, imedium = 0, ifast = 0, *index_slow, *index_medium, *index_fast, islowbuffer = 0, *index_slowbuffer, imediumbuffer = 0, *index_mediumbuffer;
1091   PetscBool         view_final = PETSC_FALSE;
1092   PetscReal         ptime;
1093 
1094   PetscFunctionBeginUser;
1095   PetscCall(PetscInitialize(&argc, &argv, 0, help));
1096   comm = PETSC_COMM_WORLD;
1097   PetscCall(PetscMemzero(&ctx, sizeof(ctx)));
1098 
1099   /* Register limiters to be available on the command line */
1100   PetscCall(PetscFunctionListAdd(&limiters, "upwind", Limit3_Upwind));
1101   PetscCall(PetscFunctionListAdd(&limiters, "lax-wendroff", Limit3_LaxWendroff));
1102   PetscCall(PetscFunctionListAdd(&limiters, "beam-warming", Limit3_BeamWarming));
1103   PetscCall(PetscFunctionListAdd(&limiters, "fromm", Limit3_Fromm));
1104   PetscCall(PetscFunctionListAdd(&limiters, "minmod", Limit3_Minmod));
1105   PetscCall(PetscFunctionListAdd(&limiters, "superbee", Limit3_Superbee));
1106   PetscCall(PetscFunctionListAdd(&limiters, "mc", Limit3_MC));
1107   PetscCall(PetscFunctionListAdd(&limiters, "koren3", Limit3_Koren3));
1108 
1109   /* Register physical models to be available on the command line */
1110   PetscCall(PetscFunctionListAdd(&physics, "advect", PhysicsCreate_Advect));
1111 
1112   ctx.comm   = comm;
1113   ctx.cfl    = 0.9;
1114   ctx.bctype = FVBC_PERIODIC;
1115   ctx.xmin   = -1.0;
1116   ctx.xmax   = 1.0;
1117   PetscOptionsBegin(comm, NULL, "Finite Volume solver options", "");
1118   PetscCall(PetscOptionsReal("-xmin", "X min", "", ctx.xmin, &ctx.xmin, NULL));
1119   PetscCall(PetscOptionsReal("-xmax", "X max", "", ctx.xmax, &ctx.xmax, NULL));
1120   PetscCall(PetscOptionsFList("-limit", "Name of flux imiter to use", "", limiters, lname, lname, sizeof(lname), NULL));
1121   PetscCall(PetscOptionsInt("-draw", "Draw solution vector, bitwise OR of (1=initial,2=final,4=final error)", "", draw, &draw, NULL));
1122   PetscCall(PetscOptionsString("-view_final", "Write final solution in ASCII MATLAB format to given file name", "", final_fname, final_fname, sizeof(final_fname), &view_final));
1123   PetscCall(PetscOptionsInt("-initial", "Initial condition (depends on the physics)", "", ctx.initial, &ctx.initial, NULL));
1124   PetscCall(PetscOptionsBool("-exact", "Compare errors with exact solution", "", ctx.exact, &ctx.exact, NULL));
1125   PetscCall(PetscOptionsBool("-simulation", "Compare errors with reference solution", "", ctx.simulation, &ctx.simulation, NULL));
1126   PetscCall(PetscOptionsReal("-cfl", "CFL number to time step at", "", ctx.cfl, &ctx.cfl, NULL));
1127   PetscCall(PetscOptionsEnum("-bc_type", "Boundary condition", "", FVBCTypes, (PetscEnum)ctx.bctype, (PetscEnum *)&ctx.bctype, NULL));
1128   PetscCall(PetscOptionsInt("-hratio", "Spacing ratio", "", ctx.hratio, &ctx.hratio, NULL));
1129   PetscOptionsEnd();
1130 
1131   /* Choose the limiter from the list of registered limiters */
1132   PetscCall(PetscFunctionListFind(limiters, lname, &ctx.limit3));
1133   PetscCheck(ctx.limit3, PETSC_COMM_SELF, PETSC_ERR_ARG_UNKNOWN_TYPE, "Limiter '%s' not found", lname);
1134 
1135   /* Choose the physics from the list of registered models */
1136   {
1137     PetscErrorCode (*r)(FVCtx *);
1138     PetscCall(PetscFunctionListFind(physics, physname, &r));
1139     PetscCheck(r, PETSC_COMM_SELF, PETSC_ERR_ARG_UNKNOWN_TYPE, "Physics '%s' not found", physname);
1140     /* Create the physics, will set the number of fields and their names */
1141     PetscCall((*r)(&ctx));
1142   }
1143 
1144   /* Create a DMDA to manage the parallel grid */
1145   PetscCall(DMDACreate1d(comm, DM_BOUNDARY_PERIODIC, 50, ctx.physics2.dof, 2, NULL, &da));
1146   PetscCall(DMSetFromOptions(da));
1147   PetscCall(DMSetUp(da));
1148   /* Inform the DMDA of the field names provided by the physics. */
1149   /* The names will be shown in the title bars when run with -ts_monitor_draw_solution */
1150   for (i = 0; i < ctx.physics2.dof; i++) PetscCall(DMDASetFieldName(da, i, ctx.physics2.fieldname[i]));
1151   PetscCall(DMDAGetInfo(da, 0, &Mx, 0, 0, 0, 0, 0, &dof, 0, 0, 0, 0, 0));
1152   PetscCall(DMDAGetCorners(da, &xs, 0, 0, &xm, 0, 0));
1153 
1154   /* Set coordinates of cell centers */
1155   PetscCall(DMDASetUniformCoordinates(da, ctx.xmin + 0.5 * (ctx.xmax - ctx.xmin) / Mx, ctx.xmax + 0.5 * (ctx.xmax - ctx.xmin) / Mx, 0, 0, 0, 0));
1156 
1157   /* Allocate work space for the Finite Volume solver (so it doesn't have to be reallocated on each function evaluation) */
1158   PetscCall(PetscMalloc4(dof * dof, &ctx.R, dof * dof, &ctx.Rinv, 2 * dof, &ctx.cjmpLR, 1 * dof, &ctx.cslope));
1159   PetscCall(PetscMalloc3(2 * dof, &ctx.uLR, dof, &ctx.flux, dof, &ctx.speeds));
1160 
1161   /* Create a vector to store the solution and to save the initial state */
1162   PetscCall(DMCreateGlobalVector(da, &X));
1163   PetscCall(VecDuplicate(X, &X0));
1164   PetscCall(VecDuplicate(X, &R));
1165 
1166   /* create index for slow parts and fast parts,
1167      count_slow + count_fast = Mx, counts_slow*hs = 0.5, counts_fast*hf = 0.5 */
1168   count_slow   = Mx / (1 + ctx.hratio) / (1 + ctx.hratio);
1169   count_medium = 2 * ctx.hratio * count_slow;
1170   PetscCheck((count_slow % 2) == 0 && (count_medium % 2) == 0, PETSC_COMM_WORLD, PETSC_ERR_USER, "Please adjust grid size Mx (-da_grid_x) and hratio (-hratio) so that Mx/(1+hartio)^2 and Mx*2*hratio/(1+hratio)^2 is even");
1171   count_fast = ctx.hratio * ctx.hratio * count_slow;
1172   ctx.sm     = count_slow / 2;
1173   ctx.mf     = ctx.sm + count_medium / 2;
1174   ctx.fm     = ctx.mf + count_fast;
1175   ctx.ms     = ctx.fm + count_medium / 2;
1176   PetscCall(PetscMalloc1(xm * dof, &index_slow));
1177   PetscCall(PetscMalloc1(xm * dof, &index_medium));
1178   PetscCall(PetscMalloc1(xm * dof, &index_fast));
1179   PetscCall(PetscMalloc1(6 * dof, &index_slowbuffer));
1180   PetscCall(PetscMalloc1(6 * dof, &index_mediumbuffer));
1181   if (((AdvectCtx *)ctx.physics2.user)->a > 0) {
1182     ctx.lsbwidth = 2;
1183     ctx.rsbwidth = 4;
1184     ctx.lmbwidth = 2;
1185     ctx.rmbwidth = 4;
1186   } else {
1187     ctx.lsbwidth = 4;
1188     ctx.rsbwidth = 2;
1189     ctx.lmbwidth = 4;
1190     ctx.rmbwidth = 2;
1191   }
1192 
1193   for (i = xs; i < xs + xm; i++) {
1194     if (i < ctx.sm - ctx.lsbwidth || i > ctx.ms + ctx.rsbwidth - 1)
1195       for (k = 0; k < dof; k++) index_slow[islow++] = i * dof + k;
1196     else if ((i >= ctx.sm - ctx.lsbwidth && i < ctx.sm) || (i > ctx.ms - 1 && i <= ctx.ms + ctx.rsbwidth - 1))
1197       for (k = 0; k < dof; k++) index_slowbuffer[islowbuffer++] = i * dof + k;
1198     else if (i < ctx.mf - ctx.lmbwidth || i > ctx.fm + ctx.rmbwidth - 1)
1199       for (k = 0; k < dof; k++) index_medium[imedium++] = i * dof + k;
1200     else if ((i >= ctx.mf - ctx.lmbwidth && i < ctx.mf) || (i > ctx.fm - 1 && i <= ctx.fm + ctx.rmbwidth - 1))
1201       for (k = 0; k < dof; k++) index_mediumbuffer[imediumbuffer++] = i * dof + k;
1202     else
1203       for (k = 0; k < dof; k++) index_fast[ifast++] = i * dof + k;
1204   }
1205   PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, islow, index_slow, PETSC_COPY_VALUES, &ctx.iss));
1206   PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, imedium, index_medium, PETSC_COPY_VALUES, &ctx.ism));
1207   PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, ifast, index_fast, PETSC_COPY_VALUES, &ctx.isf));
1208   PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, islowbuffer, index_slowbuffer, PETSC_COPY_VALUES, &ctx.issb));
1209   PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, imediumbuffer, index_mediumbuffer, PETSC_COPY_VALUES, &ctx.ismb));
1210 
1211   /* Create a time-stepping object */
1212   PetscCall(TSCreate(comm, &ts));
1213   PetscCall(TSSetDM(ts, da));
1214   PetscCall(TSSetRHSFunction(ts, R, FVRHSFunction_3WaySplit, &ctx));
1215   PetscCall(TSRHSSplitSetIS(ts, "slow", ctx.iss));
1216   PetscCall(TSRHSSplitSetIS(ts, "medium", ctx.ism));
1217   PetscCall(TSRHSSplitSetIS(ts, "fast", ctx.isf));
1218   PetscCall(TSRHSSplitSetIS(ts, "slowbuffer", ctx.issb));
1219   PetscCall(TSRHSSplitSetIS(ts, "mediumbuffer", ctx.ismb));
1220   PetscCall(TSRHSSplitSetRHSFunction(ts, "slow", NULL, FVRHSFunctionslow_3WaySplit, &ctx));
1221   PetscCall(TSRHSSplitSetRHSFunction(ts, "medium", NULL, FVRHSFunctionmedium_3WaySplit, &ctx));
1222   PetscCall(TSRHSSplitSetRHSFunction(ts, "fast", NULL, FVRHSFunctionfast_3WaySplit, &ctx));
1223   PetscCall(TSRHSSplitSetRHSFunction(ts, "slowbuffer", NULL, FVRHSFunctionslowbuffer_3WaySplit, &ctx));
1224   PetscCall(TSRHSSplitSetRHSFunction(ts, "mediumbuffer", NULL, FVRHSFunctionmediumbuffer_3WaySplit, &ctx));
1225 
1226   PetscCall(TSSetType(ts, TSSSP));
1227   /*PetscCall(TSSetType(ts,TSMPRK));*/
1228   PetscCall(TSSetMaxTime(ts, 10));
1229   PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_STEPOVER));
1230 
1231   /* Compute initial conditions and starting time step */
1232   PetscCall(FVSample_3WaySplit(&ctx, da, 0, X0));
1233   PetscCall(FVRHSFunction_3WaySplit(ts, 0, X0, X, (void *)&ctx)); /* Initial function evaluation, only used to determine max speed */
1234   PetscCall(VecCopy(X0, X));                                      /* The function value was not used so we set X=X0 again */
1235   PetscCall(TSSetTimeStep(ts, ctx.cfl / ctx.cfl_idt));
1236   PetscCall(TSSetFromOptions(ts)); /* Take runtime options */
1237   PetscCall(SolutionStatsView(da, X, PETSC_VIEWER_STDOUT_WORLD));
1238   {
1239     PetscInt           steps;
1240     PetscScalar        mass_initial, mass_final, mass_difference, mass_differenceg;
1241     const PetscScalar *ptr_X, *ptr_X0;
1242     const PetscReal    hs = (ctx.xmax - ctx.xmin) / 4.0 / count_slow;
1243     const PetscReal    hm = (ctx.xmax - ctx.xmin) / 2.0 / count_medium;
1244     const PetscReal    hf = (ctx.xmax - ctx.xmin) / 4.0 / count_fast;
1245 
1246     PetscCall(TSSolve(ts, X));
1247     PetscCall(TSGetSolveTime(ts, &ptime));
1248     PetscCall(TSGetStepNumber(ts, &steps));
1249     /* calculate the total mass at initial time and final time */
1250     mass_initial = 0.0;
1251     mass_final   = 0.0;
1252     PetscCall(DMDAVecGetArrayRead(da, X0, (void *)&ptr_X0));
1253     PetscCall(DMDAVecGetArrayRead(da, X, (void *)&ptr_X));
1254     for (i = xs; i < xs + xm; i++) {
1255       if (i < ctx.sm || i > ctx.ms - 1)
1256         for (k = 0; k < dof; k++) {
1257           mass_initial = mass_initial + hs * ptr_X0[i * dof + k];
1258           mass_final   = mass_final + hs * ptr_X[i * dof + k];
1259         }
1260       else if (i < ctx.mf || i > ctx.fm - 1)
1261         for (k = 0; k < dof; k++) {
1262           mass_initial = mass_initial + hm * ptr_X0[i * dof + k];
1263           mass_final   = mass_final + hm * ptr_X[i * dof + k];
1264         }
1265       else {
1266         for (k = 0; k < dof; k++) {
1267           mass_initial = mass_initial + hf * ptr_X0[i * dof + k];
1268           mass_final   = mass_final + hf * ptr_X[i * dof + k];
1269         }
1270       }
1271     }
1272     PetscCall(DMDAVecRestoreArrayRead(da, X0, (void *)&ptr_X0));
1273     PetscCall(DMDAVecRestoreArrayRead(da, X, (void *)&ptr_X));
1274     mass_difference = mass_final - mass_initial;
1275     PetscCallMPI(MPIU_Allreduce(&mass_difference, &mass_differenceg, 1, MPIU_SCALAR, MPIU_SUM, comm));
1276     PetscCall(PetscPrintf(comm, "Mass difference %g\n", (double)mass_differenceg));
1277     PetscCall(PetscPrintf(comm, "Final time %g, steps %" PetscInt_FMT "\n", (double)ptime, steps));
1278     PetscCall(PetscPrintf(comm, "Maximum allowable stepsize according to CFL %g\n", (double)(1 / ctx.cfl_idt)));
1279     if (ctx.exact) {
1280       PetscReal nrm1 = 0;
1281       PetscCall(SolutionErrorNorms_3WaySplit(&ctx, da, ptime, X, &nrm1));
1282       PetscCall(PetscPrintf(comm, "Error ||x-x_e||_1 %g\n", (double)nrm1));
1283     }
1284     if (ctx.simulation) {
1285       PetscReal          nrm1 = 0;
1286       PetscViewer        fd;
1287       char               filename[PETSC_MAX_PATH_LEN] = "binaryoutput";
1288       Vec                XR;
1289       PetscBool          flg;
1290       const PetscScalar *ptr_XR;
1291       PetscCall(PetscOptionsGetString(NULL, NULL, "-f", filename, sizeof(filename), &flg));
1292       PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_USER, "Must indicate binary file with the -f option");
1293       PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, filename, FILE_MODE_READ, &fd));
1294       PetscCall(VecDuplicate(X0, &XR));
1295       PetscCall(VecLoad(XR, fd));
1296       PetscCall(PetscViewerDestroy(&fd));
1297       PetscCall(VecGetArrayRead(X, &ptr_X));
1298       PetscCall(VecGetArrayRead(XR, &ptr_XR));
1299       for (i = xs; i < xs + xm; i++) {
1300         if (i < ctx.sm || i > ctx.ms - 1)
1301           for (k = 0; k < dof; k++) nrm1 = nrm1 + hs * PetscAbs(ptr_X[i * dof + k] - ptr_XR[i * dof + k]);
1302         else if (i < ctx.mf || i < ctx.fm - 1)
1303           for (k = 0; k < dof; k++) nrm1 = nrm1 + hm * PetscAbs(ptr_X[i * dof + k] - ptr_XR[i * dof + k]);
1304         else
1305           for (k = 0; k < dof; k++) nrm1 = nrm1 + hf * PetscAbs(ptr_X[i * dof + k] - ptr_XR[i * dof + k]);
1306       }
1307       PetscCall(VecRestoreArrayRead(X, &ptr_X));
1308       PetscCall(VecRestoreArrayRead(XR, &ptr_XR));
1309       PetscCall(PetscPrintf(comm, "Error ||x-x_e||_1 %g\n", (double)nrm1));
1310       PetscCall(VecDestroy(&XR));
1311     }
1312   }
1313 
1314   PetscCall(SolutionStatsView(da, X, PETSC_VIEWER_STDOUT_WORLD));
1315   if (draw & 0x1) PetscCall(VecView(X0, PETSC_VIEWER_DRAW_WORLD));
1316   if (draw & 0x2) PetscCall(VecView(X, PETSC_VIEWER_DRAW_WORLD));
1317   if (draw & 0x4) {
1318     Vec Y;
1319     PetscCall(VecDuplicate(X, &Y));
1320     PetscCall(FVSample_3WaySplit(&ctx, da, ptime, Y));
1321     PetscCall(VecAYPX(Y, -1, X));
1322     PetscCall(VecView(Y, PETSC_VIEWER_DRAW_WORLD));
1323     PetscCall(VecDestroy(&Y));
1324   }
1325 
1326   if (view_final) {
1327     PetscViewer viewer;
1328     PetscCall(PetscViewerASCIIOpen(PETSC_COMM_WORLD, final_fname, &viewer));
1329     PetscCall(PetscViewerPushFormat(viewer, PETSC_VIEWER_ASCII_MATLAB));
1330     PetscCall(VecView(X, viewer));
1331     PetscCall(PetscViewerPopFormat(viewer));
1332     PetscCall(PetscViewerDestroy(&viewer));
1333   }
1334 
1335   /* Clean up */
1336   PetscCall((*ctx.physics2.destroy)(ctx.physics2.user));
1337   for (i = 0; i < ctx.physics2.dof; i++) PetscCall(PetscFree(ctx.physics2.fieldname[i]));
1338   PetscCall(PetscFree4(ctx.R, ctx.Rinv, ctx.cjmpLR, ctx.cslope));
1339   PetscCall(PetscFree3(ctx.uLR, ctx.flux, ctx.speeds));
1340   PetscCall(VecDestroy(&X));
1341   PetscCall(VecDestroy(&X0));
1342   PetscCall(VecDestroy(&R));
1343   PetscCall(DMDestroy(&da));
1344   PetscCall(TSDestroy(&ts));
1345   PetscCall(ISDestroy(&ctx.iss));
1346   PetscCall(ISDestroy(&ctx.ism));
1347   PetscCall(ISDestroy(&ctx.isf));
1348   PetscCall(ISDestroy(&ctx.issb));
1349   PetscCall(ISDestroy(&ctx.ismb));
1350   PetscCall(PetscFree(index_slow));
1351   PetscCall(PetscFree(index_medium));
1352   PetscCall(PetscFree(index_fast));
1353   PetscCall(PetscFree(index_slowbuffer));
1354   PetscCall(PetscFree(index_mediumbuffer));
1355   PetscCall(PetscFunctionListDestroy(&limiters));
1356   PetscCall(PetscFunctionListDestroy(&physics));
1357   PetscCall(PetscFinalize());
1358   return 0;
1359 }
1360 
1361 /*TEST
1362 
1363     build:
1364       requires: !complex
1365       depends: finitevolume1d.c
1366 
1367     test:
1368       suffix: 1
1369       args: -da_grid_x 90 -initial 7 -xmin -1 -xmax 1 -hratio 2 -limit mc -ts_time_step 0.025 -ts_max_steps 24 -ts_type mprk -ts_mprk_type 2a23 -ts_use_splitrhsfunction 0
1370 
1371     test:
1372       suffix: 2
1373       args: -da_grid_x 90 -initial 7 -xmin -1 -xmax 1 -hratio 2 -limit mc -ts_time_step 0.025 -ts_max_steps 24 -ts_type mprk -ts_mprk_type 2a23 -ts_use_splitrhsfunction 1
1374 
1375 TEST*/
1376