Actual source code: posindep.c

petsc-3.4.4 2014-03-13
  1: /*
  2:        Code for Timestepping with implicit backwards Euler.
  3: */
  4: #include <petsc-private/tsimpl.h>                /*I   "petscts.h"   I*/

  6: typedef struct {
  7:   Vec update;       /* work vector where new solution is formed */
  8:   Vec func;         /* work vector where F(t[i],u[i]) is stored */
  9:   Vec xdot;         /* work vector for time derivative of state */

 11:   /* information used for Pseudo-timestepping */

 13:   PetscErrorCode (*dt)(TS,PetscReal*,void*);              /* compute next timestep, and related context */
 14:   void *dtctx;
 15:   PetscErrorCode (*verify)(TS,Vec,void*,PetscReal*,PetscBool*);  /* verify previous timestep and related context */
 16:   void *verifyctx;

 18:   PetscReal fnorm_initial,fnorm;                   /* original and current norm of F(u) */
 19:   PetscReal fnorm_previous;

 21:   PetscReal dt_initial;                     /* initial time-step */
 22:   PetscReal dt_increment;                   /* scaling that dt is incremented each time-step */
 23:   PetscReal dt_max;                         /* maximum time step */
 24:   PetscBool increment_dt_from_initial_dt;
 25: } TS_Pseudo;

 27: /* ------------------------------------------------------------------------------*/

 31: /*@C
 32:     TSPseudoComputeTimeStep - Computes the next timestep for a currently running
 33:     pseudo-timestepping process.

 35:     Collective on TS

 37:     Input Parameter:
 38: .   ts - timestep context

 40:     Output Parameter:
 41: .   dt - newly computed timestep

 43:     Level: developer

 45:     Notes:
 46:     The routine to be called here to compute the timestep should be
 47:     set by calling TSPseudoSetTimeStep().

 49: .keywords: timestep, pseudo, compute

 51: .seealso: TSPseudoTimeStepDefault(), TSPseudoSetTimeStep()
 52: @*/
 53: PetscErrorCode  TSPseudoComputeTimeStep(TS ts,PetscReal *dt)
 54: {
 55:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;

 59:   PetscLogEventBegin(TS_PseudoComputeTimeStep,ts,0,0,0);
 60:   (*pseudo->dt)(ts,dt,pseudo->dtctx);
 61:   PetscLogEventEnd(TS_PseudoComputeTimeStep,ts,0,0,0);
 62:   return(0);
 63: }


 66: /* ------------------------------------------------------------------------------*/
 69: /*@C
 70:    TSPseudoVerifyTimeStepDefault - Default code to verify the quality of the last timestep.

 72:    Collective on TS

 74:    Input Parameters:
 75: +  ts - the timestep context
 76: .  dtctx - unused timestep context
 77: -  update - latest solution vector

 79:    Output Parameters:
 80: +  newdt - the timestep to use for the next step
 81: -  flag - flag indicating whether the last time step was acceptable

 83:    Level: advanced

 85:    Note:
 86:    This routine always returns a flag of 1, indicating an acceptable
 87:    timestep.

 89: .keywords: timestep, pseudo, default, verify

 91: .seealso: TSPseudoSetVerifyTimeStep(), TSPseudoVerifyTimeStep()
 92: @*/
 93: PetscErrorCode  TSPseudoVerifyTimeStepDefault(TS ts,Vec update,void *dtctx,PetscReal *newdt,PetscBool  *flag)
 94: {
 96:   *flag = PETSC_TRUE;
 97:   return(0);
 98: }


103: /*@
104:     TSPseudoVerifyTimeStep - Verifies whether the last timestep was acceptable.

106:     Collective on TS

108:     Input Parameters:
109: +   ts - timestep context
110: -   update - latest solution vector

112:     Output Parameters:
113: +   dt - newly computed timestep (if it had to shrink)
114: -   flag - indicates if current timestep was ok

116:     Level: advanced

118:     Notes:
119:     The routine to be called here to compute the timestep should be
120:     set by calling TSPseudoSetVerifyTimeStep().

122: .keywords: timestep, pseudo, verify

124: .seealso: TSPseudoSetVerifyTimeStep(), TSPseudoVerifyTimeStepDefault()
125: @*/
126: PetscErrorCode  TSPseudoVerifyTimeStep(TS ts,Vec update,PetscReal *dt,PetscBool  *flag)
127: {
128:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;

132:   if (!pseudo->verify) {*flag = PETSC_TRUE; return(0);}

134:   (*pseudo->verify)(ts,update,pseudo->verifyctx,dt,flag);
135:   return(0);
136: }

138: /* --------------------------------------------------------------------------------*/

142: static PetscErrorCode TSStep_Pseudo(TS ts)
143: {
144:   TS_Pseudo           *pseudo = (TS_Pseudo*)ts->data;
145:   PetscInt            its,lits,reject;
146:   PetscBool           stepok;
147:   PetscReal           next_time_step;
148:   SNESConvergedReason snesreason = SNES_CONVERGED_ITERATING;
149:   PetscErrorCode      ierr;

152:   if (ts->steps == 0) pseudo->dt_initial = ts->time_step;
153:   VecCopy(ts->vec_sol,pseudo->update);
154:   next_time_step = ts->time_step;
155:   TSPseudoComputeTimeStep(ts,&next_time_step);
156:   for (reject=0; reject<ts->max_reject; reject++,ts->reject++) {
157:     ts->time_step = next_time_step;
158:     TSPreStep(ts);
159:     TSPreStage(ts,ts->ptime+ts->time_step);
160:     SNESSolve(ts->snes,NULL,pseudo->update);
161:     SNESGetConvergedReason(ts->snes,&snesreason);
162:     SNESGetLinearSolveIterations(ts->snes,&lits);
163:     SNESGetIterationNumber(ts->snes,&its);
164:     ts->snes_its += its; ts->ksp_its += lits;
165:     PetscInfo3(ts,"step=%D, nonlinear solve iterations=%D, linear solve iterations=%D\n",ts->steps,its,lits);
166:     pseudo->fnorm = -1;         /* The current norm is no longer valid, monitor must recompute it. */
167:     TSPseudoVerifyTimeStep(ts,pseudo->update,&next_time_step,&stepok);
168:     if (stepok) break;
169:   }
170:   if (snesreason < 0 && ts->max_snes_failures > 0 && ++ts->num_snes_failures >= ts->max_snes_failures) {
171:     ts->reason = TS_DIVERGED_NONLINEAR_SOLVE;
172:     PetscInfo2(ts,"step=%D, nonlinear solve solve failures %D greater than current TS allowed, stopping solve\n",ts->steps,ts->num_snes_failures);
173:     return(0);
174:   }
175:   if (reject >= ts->max_reject) {
176:     ts->reason = TS_DIVERGED_STEP_REJECTED;
177:     PetscInfo2(ts,"step=%D, step rejections %D greater than current TS allowed, stopping solve\n",ts->steps,reject);
178:     return(0);
179:   }
180:   VecCopy(pseudo->update,ts->vec_sol);
181:   ts->ptime += ts->time_step;
182:   ts->time_step = next_time_step;
183:   ts->steps++;
184:   return(0);
185: }

187: /*------------------------------------------------------------*/
190: static PetscErrorCode TSReset_Pseudo(TS ts)
191: {
192:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;

196:   VecDestroy(&pseudo->update);
197:   VecDestroy(&pseudo->func);
198:   VecDestroy(&pseudo->xdot);
199:   return(0);
200: }

204: static PetscErrorCode TSDestroy_Pseudo(TS ts)
205: {

209:   TSReset_Pseudo(ts);
210:   PetscFree(ts->data);
211:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetVerifyTimeStep_C",NULL);
212:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetTimeStepIncrement_C",NULL);
213:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetMaxTimeStep_C",NULL);
214:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoIncrementDtFromInitialDt_C",NULL);
215:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetTimeStep_C",NULL);
216:   return(0);
217: }

219: /*------------------------------------------------------------*/

223: /*
224:     Compute Xdot = (X^{n+1}-X^n)/dt) = 0
225: */
226: static PetscErrorCode TSPseudoGetXdot(TS ts,Vec X,Vec *Xdot)
227: {
228:   TS_Pseudo         *pseudo = (TS_Pseudo*)ts->data;
229:   const PetscScalar mdt     = 1.0/ts->time_step,*xnp1,*xn;
230:   PetscScalar       *xdot;
231:   PetscErrorCode    ierr;
232:   PetscInt          i,n;

235:   VecGetArrayRead(ts->vec_sol,&xn);
236:   VecGetArrayRead(X,&xnp1);
237:   VecGetArray(pseudo->xdot,&xdot);
238:   VecGetLocalSize(X,&n);
239:   for (i=0; i<n; i++) xdot[i] = mdt*(xnp1[i] - xn[i]);
240:   VecRestoreArrayRead(ts->vec_sol,&xn);
241:   VecRestoreArrayRead(X,&xnp1);
242:   VecRestoreArray(pseudo->xdot,&xdot);
243:   *Xdot = pseudo->xdot;
244:   return(0);
245: }

249: /*
250:     The transient residual is

252:         F(U^{n+1},(U^{n+1}-U^n)/dt) = 0

254:     or for ODE,

256:         (U^{n+1} - U^{n})/dt - F(U^{n+1}) = 0

258:     This is the function that must be evaluated for transient simulation and for
259:     finite difference Jacobians.  On the first Newton step, this algorithm uses
260:     a guess of U^{n+1} = U^n in which case the transient term vanishes and the
261:     residual is actually the steady state residual.  Pseudotransient
262:     continuation as described in the literature is a linearly implicit
263:     algorithm, it only takes this one Newton step with the steady state
264:     residual, and then advances to the next time step.
265: */
266: static PetscErrorCode SNESTSFormFunction_Pseudo(SNES snes,Vec X,Vec Y,TS ts)
267: {
268:   Vec            Xdot;

272:   TSPseudoGetXdot(ts,X,&Xdot);
273:   TSComputeIFunction(ts,ts->ptime+ts->time_step,X,Xdot,Y,PETSC_FALSE);
274:   return(0);
275: }

279: /*
280:    This constructs the Jacobian needed for SNES.  For DAE, this is

282:        dF(X,Xdot)/dX + shift*dF(X,Xdot)/dXdot

284:     and for ODE:

286:        J = I/dt - J_{Frhs}   where J_{Frhs} is the given Jacobian of Frhs.
287: */
288: static PetscErrorCode SNESTSFormJacobian_Pseudo(SNES snes,Vec X,Mat *AA,Mat *BB,MatStructure *str,TS ts)
289: {
290:   Vec            Xdot;

294:   TSPseudoGetXdot(ts,X,&Xdot);
295:   TSComputeIJacobian(ts,ts->ptime+ts->time_step,X,Xdot,1./ts->time_step,AA,BB,str,PETSC_FALSE);
296:   return(0);
297: }


302: static PetscErrorCode TSSetUp_Pseudo(TS ts)
303: {
304:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;

308:   VecDuplicate(ts->vec_sol,&pseudo->update);
309:   VecDuplicate(ts->vec_sol,&pseudo->func);
310:   VecDuplicate(ts->vec_sol,&pseudo->xdot);
311:   return(0);
312: }
313: /*------------------------------------------------------------*/

317: PetscErrorCode TSPseudoMonitorDefault(TS ts,PetscInt step,PetscReal ptime,Vec v,void *dummy)
318: {
319:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;
321:   PetscViewer    viewer = (PetscViewer) dummy;

324:   if (!viewer) {
325:     PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)ts),&viewer);
326:   }
327:   if (pseudo->fnorm < 0) {      /* The last computed norm is stale, recompute */
328:     VecZeroEntries(pseudo->xdot);
329:     TSComputeIFunction(ts,ts->ptime,ts->vec_sol,pseudo->xdot,pseudo->func,PETSC_FALSE);
330:     VecNorm(pseudo->func,NORM_2,&pseudo->fnorm);
331:   }
332:   PetscViewerASCIIAddTab(viewer,((PetscObject)ts)->tablevel);
333:   PetscViewerASCIIPrintf(viewer,"TS %D dt %G time %G fnorm %G\n",step,ts->time_step,ptime,pseudo->fnorm);
334:   PetscViewerASCIISubtractTab(viewer,((PetscObject)ts)->tablevel);
335:   return(0);
336: }

340: static PetscErrorCode TSSetFromOptions_Pseudo(TS ts)
341: {
342:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;
344:   PetscBool      flg = PETSC_FALSE;
345:   PetscViewer    viewer;

348:   PetscOptionsHead("Pseudo-timestepping options");
349:   PetscOptionsBool("-ts_monitor_pseudo","Monitor convergence","TSPseudoMonitorDefault",flg,&flg,NULL);
350:   if (flg) {
351:     PetscViewerASCIIOpen(PetscObjectComm((PetscObject)ts),"stdout",&viewer);
352:     TSMonitorSet(ts,TSPseudoMonitorDefault,viewer,(PetscErrorCode (*)(void**))PetscViewerDestroy);
353:   }
354:   flg  = PETSC_FALSE;
355:   PetscOptionsBool("-ts_pseudo_increment_dt_from_initial_dt","Increase dt as a ratio from original dt","TSPseudoIncrementDtFromInitialDt",flg,&flg,NULL);
356:   if (flg) {
357:     TSPseudoIncrementDtFromInitialDt(ts);
358:   }
359:   PetscOptionsReal("-ts_pseudo_increment","Ratio to increase dt","TSPseudoSetTimeStepIncrement",pseudo->dt_increment,&pseudo->dt_increment,0);
360:   PetscOptionsReal("-ts_pseudo_max_dt","Maximum value for dt","TSPseudoSetMaxTimeStep",pseudo->dt_max,&pseudo->dt_max,0);

362:   SNESSetFromOptions(ts->snes);
363:   PetscOptionsTail();
364:   return(0);
365: }

369: static PetscErrorCode TSView_Pseudo(TS ts,PetscViewer viewer)
370: {

374:   SNESView(ts->snes,viewer);
375:   return(0);
376: }

378: /* ----------------------------------------------------------------------------- */
381: /*@C
382:    TSPseudoSetVerifyTimeStep - Sets a user-defined routine to verify the quality of the
383:    last timestep.

385:    Logically Collective on TS

387:    Input Parameters:
388: +  ts - timestep context
389: .  dt - user-defined function to verify timestep
390: -  ctx - [optional] user-defined context for private data
391:          for the timestep verification routine (may be NULL)

393:    Level: advanced

395:    Calling sequence of func:
396: .  func (TS ts,Vec update,void *ctx,PetscReal *newdt,PetscBool  *flag);

398: .  update - latest solution vector
399: .  ctx - [optional] timestep context
400: .  newdt - the timestep to use for the next step
401: .  flag - flag indicating whether the last time step was acceptable

403:    Notes:
404:    The routine set here will be called by TSPseudoVerifyTimeStep()
405:    during the timestepping process.

407: .keywords: timestep, pseudo, set, verify

409: .seealso: TSPseudoVerifyTimeStepDefault(), TSPseudoVerifyTimeStep()
410: @*/
411: PetscErrorCode  TSPseudoSetVerifyTimeStep(TS ts,PetscErrorCode (*dt)(TS,Vec,void*,PetscReal*,PetscBool*),void *ctx)
412: {

417:   PetscTryMethod(ts,"TSPseudoSetVerifyTimeStep_C",(TS,PetscErrorCode (*)(TS,Vec,void*,PetscReal*,PetscBool*),void*),(ts,dt,ctx));
418:   return(0);
419: }

423: /*@
424:     TSPseudoSetTimeStepIncrement - Sets the scaling increment applied to
425:     dt when using the TSPseudoTimeStepDefault() routine.

427:    Logically Collective on TS

429:     Input Parameters:
430: +   ts - the timestep context
431: -   inc - the scaling factor >= 1.0

433:     Options Database Key:
434: $    -ts_pseudo_increment <increment>

436:     Level: advanced

438: .keywords: timestep, pseudo, set, increment

440: .seealso: TSPseudoSetTimeStep(), TSPseudoTimeStepDefault()
441: @*/
442: PetscErrorCode  TSPseudoSetTimeStepIncrement(TS ts,PetscReal inc)
443: {

449:   PetscTryMethod(ts,"TSPseudoSetTimeStepIncrement_C",(TS,PetscReal),(ts,inc));
450:   return(0);
451: }

455: /*@
456:     TSPseudoSetMaxTimeStep - Sets the maximum time step
457:     when using the TSPseudoTimeStepDefault() routine.

459:    Logically Collective on TS

461:     Input Parameters:
462: +   ts - the timestep context
463: -   maxdt - the maximum time step, use a non-positive value to deactivate

465:     Options Database Key:
466: $    -ts_pseudo_max_dt <increment>

468:     Level: advanced

470: .keywords: timestep, pseudo, set

472: .seealso: TSPseudoSetTimeStep(), TSPseudoTimeStepDefault()
473: @*/
474: PetscErrorCode  TSPseudoSetMaxTimeStep(TS ts,PetscReal maxdt)
475: {

481:   PetscTryMethod(ts,"TSPseudoSetMaxTimeStep_C",(TS,PetscReal),(ts,maxdt));
482:   return(0);
483: }

487: /*@
488:     TSPseudoIncrementDtFromInitialDt - Indicates that a new timestep
489:     is computed via the formula
490: $         dt = initial_dt*initial_fnorm/current_fnorm
491:       rather than the default update,
492: $         dt = current_dt*previous_fnorm/current_fnorm.

494:    Logically Collective on TS

496:     Input Parameter:
497: .   ts - the timestep context

499:     Options Database Key:
500: $    -ts_pseudo_increment_dt_from_initial_dt

502:     Level: advanced

504: .keywords: timestep, pseudo, set, increment

506: .seealso: TSPseudoSetTimeStep(), TSPseudoTimeStepDefault()
507: @*/
508: PetscErrorCode  TSPseudoIncrementDtFromInitialDt(TS ts)
509: {

514:   PetscTryMethod(ts,"TSPseudoIncrementDtFromInitialDt_C",(TS),(ts));
515:   return(0);
516: }


521: /*@C
522:    TSPseudoSetTimeStep - Sets the user-defined routine to be
523:    called at each pseudo-timestep to update the timestep.

525:    Logically Collective on TS

527:    Input Parameters:
528: +  ts - timestep context
529: .  dt - function to compute timestep
530: -  ctx - [optional] user-defined context for private data
531:          required by the function (may be NULL)

533:    Level: intermediate

535:    Calling sequence of func:
536: .  func (TS ts,PetscReal *newdt,void *ctx);

538: .  newdt - the newly computed timestep
539: .  ctx - [optional] timestep context

541:    Notes:
542:    The routine set here will be called by TSPseudoComputeTimeStep()
543:    during the timestepping process.
544:    If not set then TSPseudoTimeStepDefault() is automatically used

546: .keywords: timestep, pseudo, set

548: .seealso: TSPseudoTimeStepDefault(), TSPseudoComputeTimeStep()
549: @*/
550: PetscErrorCode  TSPseudoSetTimeStep(TS ts,PetscErrorCode (*dt)(TS,PetscReal*,void*),void *ctx)
551: {

556:   PetscTryMethod(ts,"TSPseudoSetTimeStep_C",(TS,PetscErrorCode (*)(TS,PetscReal*,void*),void*),(ts,dt,ctx));
557:   return(0);
558: }

560: /* ----------------------------------------------------------------------------- */

562: typedef PetscErrorCode (*FCN1)(TS,Vec,void*,PetscReal*,PetscBool*);  /* force argument to next function to not be extern C*/
565: PetscErrorCode  TSPseudoSetVerifyTimeStep_Pseudo(TS ts,FCN1 dt,void *ctx)
566: {
567:   TS_Pseudo *pseudo;

570:   pseudo            = (TS_Pseudo*)ts->data;
571:   pseudo->verify    = dt;
572:   pseudo->verifyctx = ctx;
573:   return(0);
574: }

578: PetscErrorCode  TSPseudoSetTimeStepIncrement_Pseudo(TS ts,PetscReal inc)
579: {
580:   TS_Pseudo *pseudo = (TS_Pseudo*)ts->data;

583:   pseudo->dt_increment = inc;
584:   return(0);
585: }

589: PetscErrorCode  TSPseudoSetMaxTimeStep_Pseudo(TS ts,PetscReal maxdt)
590: {
591:   TS_Pseudo *pseudo = (TS_Pseudo*)ts->data;

594:   pseudo->dt_max = maxdt;
595:   return(0);
596: }

600: PetscErrorCode  TSPseudoIncrementDtFromInitialDt_Pseudo(TS ts)
601: {
602:   TS_Pseudo *pseudo = (TS_Pseudo*)ts->data;

605:   pseudo->increment_dt_from_initial_dt = PETSC_TRUE;
606:   return(0);
607: }

609: typedef PetscErrorCode (*FCN2)(TS,PetscReal*,void*); /* force argument to next function to not be extern C*/
612: PetscErrorCode  TSPseudoSetTimeStep_Pseudo(TS ts,FCN2 dt,void *ctx)
613: {
614:   TS_Pseudo *pseudo = (TS_Pseudo*)ts->data;

617:   pseudo->dt    = dt;
618:   pseudo->dtctx = ctx;
619:   return(0);
620: }

622: /* ----------------------------------------------------------------------------- */
623: /*MC
624:       TSPSEUDO - Solve steady state ODE and DAE problems with pseudo time stepping

626:   This method solves equations of the form

628: $    F(X,Xdot) = 0

630:   for steady state using the iteration

632: $    [G'] S = -F(X,0)
633: $    X += S

635:   where

637: $    G(Y) = F(Y,(Y-X)/dt)

639:   This is linearly-implicit Euler with the residual always evaluated "at steady
640:   state".  See note below.

642:   Options database keys:
643: +  -ts_pseudo_increment <real> - ratio of increase dt
644: -  -ts_pseudo_increment_dt_from_initial_dt <truth> - Increase dt as a ratio from original dt

646:   Level: beginner

648:   References:
649:   Todd S. Coffey and C. T. Kelley and David E. Keyes, Pseudotransient Continuation and Differential-Algebraic Equations, 2003.
650:   C. T. Kelley and David E. Keyes, Convergence analysis of Pseudotransient Continuation, 1998.

652:   Notes:
653:   The residual computed by this method includes the transient term (Xdot is computed instead of
654:   always being zero), but since the prediction from the last step is always the solution from the
655:   last step, on the first Newton iteration we have

657: $  Xdot = (Xpredicted - Xold)/dt = (Xold-Xold)/dt = 0

659:   Therefore, the linear system solved by the first Newton iteration is equivalent to the one
660:   described above and in the papers.  If the user chooses to perform multiple Newton iterations, the
661:   algorithm is no longer the one described in the referenced papers.

663: .seealso:  TSCreate(), TS, TSSetType()

665: M*/
668: PETSC_EXTERN PetscErrorCode TSCreate_Pseudo(TS ts)
669: {
670:   TS_Pseudo      *pseudo;
672:   SNES           snes;
673:   SNESType       stype;

676:   ts->ops->reset   = TSReset_Pseudo;
677:   ts->ops->destroy = TSDestroy_Pseudo;
678:   ts->ops->view    = TSView_Pseudo;

680:   ts->ops->setup          = TSSetUp_Pseudo;
681:   ts->ops->step           = TSStep_Pseudo;
682:   ts->ops->setfromoptions = TSSetFromOptions_Pseudo;
683:   ts->ops->snesfunction   = SNESTSFormFunction_Pseudo;
684:   ts->ops->snesjacobian   = SNESTSFormJacobian_Pseudo;

686:   TSGetSNES(ts,&snes);
687:   SNESGetType(snes,&stype);
688:   if (!stype) {SNESSetType(snes,SNESKSPONLY);}

690:   PetscNewLog(ts,TS_Pseudo,&pseudo);
691:   ts->data = (void*)pseudo;

693:   pseudo->dt_increment                 = 1.1;
694:   pseudo->increment_dt_from_initial_dt = PETSC_FALSE;
695:   pseudo->dt                           = TSPseudoTimeStepDefault;
696:   pseudo->fnorm                        = -1;

698:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetVerifyTimeStep_C",TSPseudoSetVerifyTimeStep_Pseudo);
699:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetTimeStepIncrement_C",TSPseudoSetTimeStepIncrement_Pseudo);
700:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetMaxTimeStep_C",TSPseudoSetMaxTimeStep_Pseudo);
701:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoIncrementDtFromInitialDt_C",TSPseudoIncrementDtFromInitialDt_Pseudo);
702:   PetscObjectComposeFunction((PetscObject)ts,"TSPseudoSetTimeStep_C",TSPseudoSetTimeStep_Pseudo);
703:   return(0);
704: }

708: /*@C
709:    TSPseudoTimeStepDefault - Default code to compute pseudo-timestepping.
710:    Use with TSPseudoSetTimeStep().

712:    Collective on TS

714:    Input Parameters:
715: .  ts - the timestep context
716: .  dtctx - unused timestep context

718:    Output Parameter:
719: .  newdt - the timestep to use for the next step

721:    Level: advanced

723: .keywords: timestep, pseudo, default

725: .seealso: TSPseudoSetTimeStep(), TSPseudoComputeTimeStep()
726: @*/
727: PetscErrorCode  TSPseudoTimeStepDefault(TS ts,PetscReal *newdt,void *dtctx)
728: {
729:   TS_Pseudo      *pseudo = (TS_Pseudo*)ts->data;
730:   PetscReal      inc     = pseudo->dt_increment,fnorm_previous = pseudo->fnorm_previous;

734:   VecZeroEntries(pseudo->xdot);
735:   TSComputeIFunction(ts,ts->ptime,ts->vec_sol,pseudo->xdot,pseudo->func,PETSC_FALSE);
736:   VecNorm(pseudo->func,NORM_2,&pseudo->fnorm);
737:   if (pseudo->fnorm_initial == 0.0) {
738:     /* first time through so compute initial function norm */
739:     pseudo->fnorm_initial = pseudo->fnorm;
740:     fnorm_previous        = pseudo->fnorm;
741:   }
742:   if (pseudo->fnorm == 0.0)                      *newdt = 1.e12*inc*ts->time_step;
743:   else if (pseudo->increment_dt_from_initial_dt) *newdt = inc*pseudo->dt_initial*pseudo->fnorm_initial/pseudo->fnorm;
744:   else                                           *newdt = inc*ts->time_step*fnorm_previous/pseudo->fnorm;
745:   if (pseudo->dt_max > 0) *newdt = PetscMin(*newdt,pseudo->dt_max);
746:   pseudo->fnorm_previous = pseudo->fnorm;
747:   return(0);
748: }