xref: /petsc/src/snes/impls/vi/ss/viss.c (revision cbd2c53bc8d4e32f1aab714f173fd0b4c821fa72)
1 
2 #include <../src/snes/impls/vi/ss/vissimpl.h> /*I "petscsnes.h" I*/
3 
4 /*
5   SNESVIComputeMeritFunction - Evaluates the merit function for the mixed complementarity problem.
6 
7   Input Parameter:
8 . phi - the semismooth function
9 
10   Output Parameter:
11 . merit - the merit function
12 . phinorm - ||phi||
13 
14   Notes:
15   The merit function for the mixed complementarity problem is defined as
16      merit = 0.5*phi^T*phi
17 */
18 static PetscErrorCode SNESVIComputeMeritFunction(Vec phi, PetscReal *merit,PetscReal *phinorm)
19 {
20   PetscErrorCode ierr;
21 
22   PetscFunctionBegin;
23   ierr = VecNormBegin(phi,NORM_2,phinorm);CHKERRQ(ierr);
24   ierr = VecNormEnd(phi,NORM_2,phinorm);CHKERRQ(ierr);
25 
26   *merit = 0.5*(*phinorm)*(*phinorm);
27   PetscFunctionReturn(0);
28 }
29 
30 PETSC_STATIC_INLINE PetscScalar Phi(PetscScalar a,PetscScalar b)
31 {
32   return a + b - PetscSqrtScalar(a*a + b*b);
33 }
34 
35 PETSC_STATIC_INLINE PetscScalar DPhi(PetscScalar a,PetscScalar b)
36 {
37   if ((PetscAbsScalar(a) >= 1.e-6) || (PetscAbsScalar(b) >= 1.e-6)) return 1.0 - a/ PetscSqrtScalar(a*a + b*b);
38   else return .5;
39 }
40 
41 /*
42    SNESVIComputeFunction - Reformulates a system of nonlinear equations in mixed complementarity form to a system of nonlinear equations in semismooth form.
43 
44    Input Parameters:
45 .  snes - the SNES context
46 .  X - current iterate
47 .  functx - user defined function context
48 
49    Output Parameters:
50 .  phi - Semismooth function
51 
52 */
53 static PetscErrorCode SNESVIComputeFunction(SNES snes,Vec X,Vec phi,void *functx)
54 {
55   PetscErrorCode    ierr;
56   SNES_VINEWTONSSLS *vi = (SNES_VINEWTONSSLS*)snes->data;
57   Vec               Xl  = snes->xl,Xu = snes->xu,F = snes->vec_func;
58   PetscScalar       *phi_arr,*f_arr,*l,*u;
59   const PetscScalar *x_arr;
60   PetscInt          i,nlocal;
61 
62   PetscFunctionBegin;
63   ierr = (*vi->computeuserfunction)(snes,X,F,functx);CHKERRQ(ierr);
64   ierr = VecGetLocalSize(X,&nlocal);CHKERRQ(ierr);
65   ierr = VecGetArrayRead(X,&x_arr);CHKERRQ(ierr);
66   ierr = VecGetArray(F,&f_arr);CHKERRQ(ierr);
67   ierr = VecGetArray(Xl,&l);CHKERRQ(ierr);
68   ierr = VecGetArray(Xu,&u);CHKERRQ(ierr);
69   ierr = VecGetArray(phi,&phi_arr);CHKERRQ(ierr);
70 
71   for (i=0; i < nlocal; i++) {
72     if ((PetscRealPart(l[i]) <= PETSC_NINFINITY) && (PetscRealPart(u[i]) >= PETSC_INFINITY)) { /* no constraints on variable */
73       phi_arr[i] = f_arr[i];
74     } else if (PetscRealPart(l[i]) <= PETSC_NINFINITY) {                      /* upper bound on variable only */
75       phi_arr[i] = -Phi(u[i] - x_arr[i],-f_arr[i]);
76     } else if (PetscRealPart(u[i]) >= PETSC_INFINITY) {                       /* lower bound on variable only */
77       phi_arr[i] = Phi(x_arr[i] - l[i],f_arr[i]);
78     } else if (l[i] == u[i]) {
79       phi_arr[i] = l[i] - x_arr[i];
80     } else {                                                /* both bounds on variable */
81       phi_arr[i] = Phi(x_arr[i] - l[i],-Phi(u[i] - x_arr[i],-f_arr[i]));
82     }
83   }
84 
85   ierr = VecRestoreArrayRead(X,&x_arr);CHKERRQ(ierr);
86   ierr = VecRestoreArray(F,&f_arr);CHKERRQ(ierr);
87   ierr = VecRestoreArray(Xl,&l);CHKERRQ(ierr);
88   ierr = VecRestoreArray(Xu,&u);CHKERRQ(ierr);
89   ierr = VecRestoreArray(phi,&phi_arr);CHKERRQ(ierr);
90   PetscFunctionReturn(0);
91 }
92 
93 /*
94    SNESVIComputeBsubdifferentialVectors - Computes the diagonal shift (Da) and row scaling (Db) vectors needed for the
95                                           the semismooth jacobian.
96 */
97 PetscErrorCode SNESVIComputeBsubdifferentialVectors(SNES snes,Vec X,Vec F,Mat jac,Vec Da,Vec Db)
98 {
99   PetscErrorCode ierr;
100   PetscScalar    *l,*u,*x,*f,*da,*db,da1,da2,db1,db2;
101   PetscInt       i,nlocal;
102 
103   PetscFunctionBegin;
104   ierr = VecGetArray(X,&x);CHKERRQ(ierr);
105   ierr = VecGetArray(F,&f);CHKERRQ(ierr);
106   ierr = VecGetArray(snes->xl,&l);CHKERRQ(ierr);
107   ierr = VecGetArray(snes->xu,&u);CHKERRQ(ierr);
108   ierr = VecGetArray(Da,&da);CHKERRQ(ierr);
109   ierr = VecGetArray(Db,&db);CHKERRQ(ierr);
110   ierr = VecGetLocalSize(X,&nlocal);CHKERRQ(ierr);
111 
112   for (i=0; i< nlocal; i++) {
113     if ((PetscRealPart(l[i]) <= PETSC_NINFINITY) && (PetscRealPart(u[i]) >= PETSC_INFINITY)) { /* no constraints on variable */
114       da[i] = 0;
115       db[i] = 1;
116     } else if (PetscRealPart(l[i]) <= PETSC_NINFINITY) {                     /* upper bound on variable only */
117       da[i] = DPhi(u[i] - x[i], -f[i]);
118       db[i] = DPhi(-f[i],u[i] - x[i]);
119     } else if (PetscRealPart(u[i]) >= PETSC_INFINITY) {                      /* lower bound on variable only */
120       da[i] = DPhi(x[i] - l[i], f[i]);
121       db[i] = DPhi(f[i],x[i] - l[i]);
122     } else if (l[i] == u[i]) {                              /* fixed variable */
123       da[i] = 1;
124       db[i] = 0;
125     } else {                                                /* upper and lower bounds on variable */
126       da1   = DPhi(x[i] - l[i], -Phi(u[i] - x[i], -f[i]));
127       db1   = DPhi(-Phi(u[i] - x[i], -f[i]),x[i] - l[i]);
128       da2   = DPhi(u[i] - x[i], -f[i]);
129       db2   = DPhi(-f[i],u[i] - x[i]);
130       da[i] = da1 + db1*da2;
131       db[i] = db1*db2;
132     }
133   }
134 
135   ierr = VecRestoreArray(X,&x);CHKERRQ(ierr);
136   ierr = VecRestoreArray(F,&f);CHKERRQ(ierr);
137   ierr = VecRestoreArray(snes->xl,&l);CHKERRQ(ierr);
138   ierr = VecRestoreArray(snes->xu,&u);CHKERRQ(ierr);
139   ierr = VecRestoreArray(Da,&da);CHKERRQ(ierr);
140   ierr = VecRestoreArray(Db,&db);CHKERRQ(ierr);
141   PetscFunctionReturn(0);
142 }
143 
144 /*
145    SNESVIComputeJacobian - Computes the jacobian of the semismooth function.The Jacobian for the semismooth function is an element of the B-subdifferential of the Fischer-Burmeister function for complementarity problems.
146 
147    Input Parameters:
148 .  Da       - Diagonal shift vector for the semismooth jacobian.
149 .  Db       - Row scaling vector for the semismooth jacobian.
150 
151    Output Parameters:
152 .  jac      - semismooth jacobian
153 .  jac_pre  - optional preconditioning matrix
154 
155    Notes:
156    The semismooth jacobian matrix is given by
157    jac = Da + Db*jacfun
158    where Db is the row scaling matrix stored as a vector,
159          Da is the diagonal perturbation matrix stored as a vector
160    and   jacfun is the jacobian of the original nonlinear function.
161 */
162 PetscErrorCode SNESVIComputeJacobian(Mat jac, Mat jac_pre,Vec Da, Vec Db)
163 {
164   PetscErrorCode ierr;
165 
166   /* Do row scaling  and add diagonal perturbation */
167   ierr = MatDiagonalScale(jac,Db,NULL);CHKERRQ(ierr);
168   ierr = MatDiagonalSet(jac,Da,ADD_VALUES);CHKERRQ(ierr);
169   if (jac != jac_pre) { /* If jac and jac_pre are different */
170     ierr = MatDiagonalScale(jac_pre,Db,NULL);CHKERRQ(ierr);
171     ierr = MatDiagonalSet(jac_pre,Da,ADD_VALUES);CHKERRQ(ierr);
172   }
173   PetscFunctionReturn(0);
174 }
175 
176 /*
177    SNESVIComputeMeritFunctionGradient - Computes the gradient of the merit function psi.
178 
179    Input Parameters:
180    phi - semismooth function.
181    H   - semismooth jacobian
182 
183    Output Parameters:
184    dpsi - merit function gradient
185 
186    Notes:
187   The merit function gradient is computed as follows
188         dpsi = H^T*phi
189 */
190 PetscErrorCode SNESVIComputeMeritFunctionGradient(Mat H, Vec phi, Vec dpsi)
191 {
192   PetscErrorCode ierr;
193 
194   PetscFunctionBegin;
195   ierr = MatMultTranspose(H,phi,dpsi);CHKERRQ(ierr);
196   PetscFunctionReturn(0);
197 }
198 
199 /*
200    SNESSolve_VINEWTONSSLS - Solves the complementarity problem with a semismooth Newton
201    method using a line search.
202 
203    Input Parameters:
204 .  snes - the SNES context
205 
206    Application Interface Routine: SNESSolve()
207 
208    Notes:
209    This implements essentially a semismooth Newton method with a
210    line search. The default line search does not do any line search
211    but rather takes a full Newton step.
212 
213    Developer Note: the code in this file should be slightly modified so that this routine need not exist and the SNESSolve_NEWTONLS() routine is called directly with the appropriate wrapped function and Jacobian evaluations
214 
215 */
216 PetscErrorCode SNESSolve_VINEWTONSSLS(SNES snes)
217 {
218   SNES_VINEWTONSSLS    *vi = (SNES_VINEWTONSSLS*)snes->data;
219   PetscErrorCode       ierr;
220   PetscInt             maxits,i,lits;
221   SNESLineSearchReason lssucceed;
222   PetscReal            gnorm,xnorm=0,ynorm;
223   Vec                  Y,X,F;
224   KSPConvergedReason   kspreason;
225   DM                   dm;
226   DMSNES               sdm;
227 
228   PetscFunctionBegin;
229   ierr = SNESGetDM(snes,&dm);CHKERRQ(ierr);
230   ierr = DMGetDMSNES(dm,&sdm);CHKERRQ(ierr);
231 
232   vi->computeuserfunction   = sdm->ops->computefunction;
233   sdm->ops->computefunction = SNESVIComputeFunction;
234 
235   snes->numFailures            = 0;
236   snes->numLinearSolveFailures = 0;
237   snes->reason                 = SNES_CONVERGED_ITERATING;
238 
239   maxits = snes->max_its;               /* maximum number of iterations */
240   X      = snes->vec_sol;               /* solution vector */
241   F      = snes->vec_func;              /* residual vector */
242   Y      = snes->work[0];               /* work vectors */
243 
244   ierr       = PetscObjectSAWsTakeAccess((PetscObject)snes);CHKERRQ(ierr);
245   snes->iter = 0;
246   snes->norm = 0.0;
247   ierr       = PetscObjectSAWsGrantAccess((PetscObject)snes);CHKERRQ(ierr);
248 
249   ierr = SNESVIProjectOntoBounds(snes,X);CHKERRQ(ierr);
250   ierr = SNESComputeFunction(snes,X,vi->phi);CHKERRQ(ierr);
251   if (snes->domainerror) {
252     snes->reason              = SNES_DIVERGED_FUNCTION_DOMAIN;
253     sdm->ops->computefunction = vi->computeuserfunction;
254     PetscFunctionReturn(0);
255   }
256   /* Compute Merit function */
257   ierr = SNESVIComputeMeritFunction(vi->phi,&vi->merit,&vi->phinorm);CHKERRQ(ierr);
258 
259   ierr = VecNormBegin(X,NORM_2,&xnorm);CHKERRQ(ierr);        /* xnorm <- ||x||  */
260   ierr = VecNormEnd(X,NORM_2,&xnorm);CHKERRQ(ierr);
261   SNESCheckFunctionNorm(snes,vi->merit);
262 
263   ierr       = PetscObjectSAWsTakeAccess((PetscObject)snes);CHKERRQ(ierr);
264   snes->norm = vi->phinorm;
265   ierr       = PetscObjectSAWsGrantAccess((PetscObject)snes);CHKERRQ(ierr);
266   ierr       = SNESLogConvergenceHistory(snes,vi->phinorm,0);CHKERRQ(ierr);
267   ierr       = SNESMonitor(snes,0,vi->phinorm);CHKERRQ(ierr);
268 
269   /* test convergence */
270   ierr = (*snes->ops->converged)(snes,0,0.0,0.0,vi->phinorm,&snes->reason,snes->cnvP);CHKERRQ(ierr);
271   if (snes->reason) {
272     sdm->ops->computefunction = vi->computeuserfunction;
273     PetscFunctionReturn(0);
274   }
275 
276   for (i=0; i<maxits; i++) {
277 
278     /* Call general purpose update function */
279     if (snes->ops->update) {
280       ierr = (*snes->ops->update)(snes, snes->iter);CHKERRQ(ierr);
281     }
282 
283     /* Solve J Y = Phi, where J is the semismooth jacobian */
284 
285     /* Get the jacobian -- note that the function must be the original function for snes_fd and snes_fd_color to work for this*/
286     sdm->ops->computefunction = vi->computeuserfunction;
287     ierr                      = SNESComputeJacobian(snes,X,snes->jacobian,snes->jacobian_pre);CHKERRQ(ierr);
288     SNESCheckJacobianDomainerror(snes);
289     sdm->ops->computefunction = SNESVIComputeFunction;
290 
291     /* Get the diagonal shift and row scaling vectors */
292     ierr = SNESVIComputeBsubdifferentialVectors(snes,X,F,snes->jacobian,vi->Da,vi->Db);CHKERRQ(ierr);
293     /* Compute the semismooth jacobian */
294     ierr = SNESVIComputeJacobian(snes->jacobian,snes->jacobian_pre,vi->Da,vi->Db);CHKERRQ(ierr);
295     /* Compute the merit function gradient */
296     ierr = SNESVIComputeMeritFunctionGradient(snes->jacobian,vi->phi,vi->dpsi);CHKERRQ(ierr);
297     ierr = KSPSetOperators(snes->ksp,snes->jacobian,snes->jacobian_pre);CHKERRQ(ierr);
298     ierr = KSPSolve(snes->ksp,vi->phi,Y);CHKERRQ(ierr);
299     ierr = KSPGetConvergedReason(snes->ksp,&kspreason);CHKERRQ(ierr);
300 
301     if (kspreason < 0) {
302       if (++snes->numLinearSolveFailures >= snes->maxLinearSolveFailures) {
303         ierr         = PetscInfo2(snes,"iter=%D, number linear solve failures %D greater than current SNES allowed, stopping solve\n",snes->iter,snes->numLinearSolveFailures);CHKERRQ(ierr);
304         snes->reason = SNES_DIVERGED_LINEAR_SOLVE;
305         break;
306       }
307     }
308     ierr              = KSPGetIterationNumber(snes->ksp,&lits);CHKERRQ(ierr);
309     snes->linear_its += lits;
310     ierr              = PetscInfo2(snes,"iter=%D, linear solve iterations=%D\n",snes->iter,lits);CHKERRQ(ierr);
311     /*
312     if (snes->ops->precheck) {
313       PetscBool changed_y = PETSC_FALSE;
314       ierr = (*snes->ops->precheck)(snes,X,Y,snes->precheck,&changed_y);CHKERRQ(ierr);
315     }
316 
317     if (PetscLogPrintInfo) {
318       ierr = SNESVICheckResidual_Private(snes,snes->jacobian,F,Y,G,W);CHKERRQ(ierr);
319     }
320     */
321     /* Compute a (scaled) negative update in the line search routine:
322          Y <- X - lambda*Y
323        and evaluate G = function(Y) (depends on the line search).
324     */
325     ierr  = VecCopy(Y,snes->vec_sol_update);CHKERRQ(ierr);
326     ynorm = 1; gnorm = vi->phinorm;
327     ierr = SNESLineSearchApply(snes->linesearch, X, vi->phi, &gnorm, Y);CHKERRQ(ierr);
328     ierr = SNESLineSearchGetReason(snes->linesearch, &lssucceed);CHKERRQ(ierr);
329     ierr = SNESLineSearchGetNorms(snes->linesearch, &xnorm, &gnorm, &ynorm);CHKERRQ(ierr);
330     ierr = PetscInfo4(snes,"fnorm=%18.16e, gnorm=%18.16e, ynorm=%18.16e, lssucceed=%d\n",(double)vi->phinorm,(double)gnorm,(double)ynorm,(int)lssucceed);CHKERRQ(ierr);
331     if (snes->reason == SNES_DIVERGED_FUNCTION_COUNT) break;
332     if (snes->domainerror) {
333       snes->reason              = SNES_DIVERGED_FUNCTION_DOMAIN;
334       sdm->ops->computefunction = vi->computeuserfunction;
335       PetscFunctionReturn(0);
336     }
337     if (lssucceed) {
338       if (++snes->numFailures >= snes->maxFailures) {
339         PetscBool ismin;
340         snes->reason = SNES_DIVERGED_LINE_SEARCH;
341         ierr         = SNESVICheckLocalMin_Private(snes,snes->jacobian,vi->phi,X,gnorm,&ismin);CHKERRQ(ierr);
342         if (ismin) snes->reason = SNES_DIVERGED_LOCAL_MIN;
343         break;
344       }
345     }
346     /* Update function and solution vectors */
347     vi->phinorm = gnorm;
348     vi->merit   = 0.5*vi->phinorm*vi->phinorm;
349     /* Monitor convergence */
350     ierr       = PetscObjectSAWsTakeAccess((PetscObject)snes);CHKERRQ(ierr);
351     snes->iter = i+1;
352     snes->norm = vi->phinorm;
353     snes->xnorm = xnorm;
354     snes->ynorm = ynorm;
355     ierr       = PetscObjectSAWsGrantAccess((PetscObject)snes);CHKERRQ(ierr);
356     ierr       = SNESLogConvergenceHistory(snes,snes->norm,lits);CHKERRQ(ierr);
357     ierr       = SNESMonitor(snes,snes->iter,snes->norm);CHKERRQ(ierr);
358     /* Test for convergence, xnorm = || X || */
359     if (snes->ops->converged != SNESConvergedSkip) { ierr = VecNorm(X,NORM_2,&xnorm);CHKERRQ(ierr); }
360     ierr = (*snes->ops->converged)(snes,snes->iter,xnorm,ynorm,vi->phinorm,&snes->reason,snes->cnvP);CHKERRQ(ierr);
361     if (snes->reason) break;
362   }
363   if (i == maxits) {
364     ierr = PetscInfo1(snes,"Maximum number of iterations has been reached: %D\n",maxits);CHKERRQ(ierr);
365     if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
366   }
367   sdm->ops->computefunction = vi->computeuserfunction;
368   PetscFunctionReturn(0);
369 }
370 
371 /* -------------------------------------------------------------------------- */
372 /*
373    SNESSetUp_VINEWTONSSLS - Sets up the internal data structures for the later use
374    of the SNES nonlinear solver.
375 
376    Input Parameter:
377 .  snes - the SNES context
378 
379    Application Interface Routine: SNESSetUp()
380 
381    Notes:
382    For basic use of the SNES solvers, the user need not explicitly call
383    SNESSetUp(), since these actions will automatically occur during
384    the call to SNESSolve().
385  */
386 PetscErrorCode SNESSetUp_VINEWTONSSLS(SNES snes)
387 {
388   PetscErrorCode    ierr;
389   SNES_VINEWTONSSLS *vi = (SNES_VINEWTONSSLS*) snes->data;
390 
391   PetscFunctionBegin;
392   ierr = SNESSetUp_VI(snes);CHKERRQ(ierr);
393   ierr = VecDuplicate(snes->vec_sol, &vi->dpsi);CHKERRQ(ierr);
394   ierr = VecDuplicate(snes->vec_sol, &vi->phi);CHKERRQ(ierr);
395   ierr = VecDuplicate(snes->vec_sol, &vi->Da);CHKERRQ(ierr);
396   ierr = VecDuplicate(snes->vec_sol, &vi->Db);CHKERRQ(ierr);
397   ierr = VecDuplicate(snes->vec_sol, &vi->z);CHKERRQ(ierr);
398   ierr = VecDuplicate(snes->vec_sol, &vi->t);CHKERRQ(ierr);
399   PetscFunctionReturn(0);
400 }
401 /* -------------------------------------------------------------------------- */
402 PetscErrorCode SNESReset_VINEWTONSSLS(SNES snes)
403 {
404   SNES_VINEWTONSSLS *vi = (SNES_VINEWTONSSLS*) snes->data;
405   PetscErrorCode    ierr;
406 
407   PetscFunctionBegin;
408   ierr = SNESReset_VI(snes);CHKERRQ(ierr);
409   ierr = VecDestroy(&vi->dpsi);CHKERRQ(ierr);
410   ierr = VecDestroy(&vi->phi);CHKERRQ(ierr);
411   ierr = VecDestroy(&vi->Da);CHKERRQ(ierr);
412   ierr = VecDestroy(&vi->Db);CHKERRQ(ierr);
413   ierr = VecDestroy(&vi->z);CHKERRQ(ierr);
414   ierr = VecDestroy(&vi->t);CHKERRQ(ierr);
415   PetscFunctionReturn(0);
416 }
417 
418 /* -------------------------------------------------------------------------- */
419 /*
420    SNESSetFromOptions_VINEWTONSSLS - Sets various parameters for the SNESVI method.
421 
422    Input Parameter:
423 .  snes - the SNES context
424 
425    Application Interface Routine: SNESSetFromOptions()
426 */
427 static PetscErrorCode SNESSetFromOptions_VINEWTONSSLS(PetscOptionItems *PetscOptionsObject,SNES snes)
428 {
429   PetscErrorCode ierr;
430 
431   PetscFunctionBegin;
432   ierr = SNESSetFromOptions_VI(PetscOptionsObject,snes);CHKERRQ(ierr);
433   ierr = PetscOptionsHead(PetscOptionsObject,"SNES semismooth method options");CHKERRQ(ierr);
434   ierr = PetscOptionsTail();CHKERRQ(ierr);
435   PetscFunctionReturn(0);
436 }
437 
438 /* -------------------------------------------------------------------------- */
439 /*MC
440       SNESVINEWTONSSLS - Semi-smooth solver for variational inequalities based on Newton's method
441 
442    Options Database:
443 +   -snes_type <vinewtonssls,vinewtonrsls> a semi-smooth solver, a reduced space active set method
444 -   -snes_vi_monitor - prints the number of active constraints at each iteration.
445 
446    Level: beginner
447 
448    References:
449 +  1. -  T. S. Munson, F. Facchinei, M. C. Ferris, A. Fischer, and C. Kanzow. The semismooth
450      algorithm for large scale complementarity problems. INFORMS Journal on Computing, 13 (2001).
451 -  2. -  T. S. Munson, and S. Benson. Flexible Complementarity Solvers for Large Scale
452      Applications, Optimization Methods and Software, 21 (2006).
453 
454 .seealso:  SNESVISetVariableBounds(), SNESVISetComputeVariableBounds(), SNESCreate(), SNES, SNESSetType(), SNESVINEWTONRSLS, SNESNEWTONTR, SNESLineSearchSetType(),SNESLineSearchSetPostCheck(), SNESLineSearchSetPreCheck()
455 
456 M*/
457 PETSC_EXTERN PetscErrorCode SNESCreate_VINEWTONSSLS(SNES snes)
458 {
459   PetscErrorCode    ierr;
460   SNES_VINEWTONSSLS *vi;
461   SNESLineSearch    linesearch;
462 
463   PetscFunctionBegin;
464   snes->ops->reset          = SNESReset_VINEWTONSSLS;
465   snes->ops->setup          = SNESSetUp_VINEWTONSSLS;
466   snes->ops->solve          = SNESSolve_VINEWTONSSLS;
467   snes->ops->destroy        = SNESDestroy_VI;
468   snes->ops->setfromoptions = SNESSetFromOptions_VINEWTONSSLS;
469   snes->ops->view           = NULL;
470 
471   snes->usesksp = PETSC_TRUE;
472   snes->usesnpc = PETSC_FALSE;
473 
474   ierr = SNESGetLineSearch(snes, &linesearch);CHKERRQ(ierr);
475   if (!((PetscObject)linesearch)->type_name) {
476     ierr = SNESLineSearchSetType(linesearch, SNESLINESEARCHBT);CHKERRQ(ierr);
477     ierr = SNESLineSearchBTSetAlpha(linesearch, 0.0);CHKERRQ(ierr);
478   }
479 
480   snes->alwayscomputesfinalresidual = PETSC_FALSE;
481 
482   ierr       = PetscNewLog(snes,&vi);CHKERRQ(ierr);
483   snes->data = (void*)vi;
484 
485   ierr = PetscObjectComposeFunction((PetscObject)snes,"SNESVISetVariableBounds_C",SNESVISetVariableBounds_VI);CHKERRQ(ierr);
486   ierr = PetscObjectComposeFunction((PetscObject)snes,"SNESVISetComputeVariableBounds_C",SNESVISetComputeVariableBounds_VI);CHKERRQ(ierr);
487   PetscFunctionReturn(0);
488 }
489 
490