Actual source code: posindep.c
petsc-3.4.5 2014-06-29
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: }