Actual source code: alpha.c

petsc-3.4.4 2014-03-13
  1: /*
  2:   Code for timestepping with implicit generalized-\alpha method
  3:   for first order systems.
  4: */
  5: #include <petsc-private/tsimpl.h>                /*I   "petscts.h"   I*/

  7: typedef PetscErrorCode (*TSAlphaAdaptFunction)(TS,PetscReal,Vec,Vec,PetscReal*,PetscBool*,void*);

  9: typedef struct {
 10:   Vec       X0,Xa,X1;
 11:   Vec       V0,Va,V1;
 12:   Vec       R,E;
 13:   PetscReal Alpha_m;
 14:   PetscReal Alpha_f;
 15:   PetscReal Gamma;
 16:   PetscReal stage_time;
 17:   PetscReal shift;

 19:   TSAlphaAdaptFunction adapt;
 20:   void                 *adaptctx;
 21:   PetscReal            rtol;
 22:   PetscReal            atol;
 23:   PetscReal            rho;
 24:   PetscReal            scale_min;
 25:   PetscReal            scale_max;
 26:   PetscReal            dt_min;
 27:   PetscReal            dt_max;
 28: } TS_Alpha;

 32: static PetscErrorCode TSStep_Alpha(TS ts)
 33: {
 34:   TS_Alpha            *th = (TS_Alpha*)ts->data;
 35:   PetscInt            its,lits,reject;
 36:   PetscReal           next_time_step;
 37:   SNESConvergedReason snesreason = SNES_CONVERGED_ITERATING;
 38:   PetscErrorCode      ierr;

 41:   if (ts->steps == 0) {
 42:     VecSet(th->V0,0.0);
 43:   } else {
 44:     VecCopy(th->V1,th->V0);
 45:   }
 46:   VecCopy(ts->vec_sol,th->X0);
 47:   next_time_step = ts->time_step;
 48:   for (reject=0; reject<ts->max_reject; reject++,ts->reject++) {
 49:     ts->time_step  = next_time_step;
 50:     th->stage_time = ts->ptime + th->Alpha_f*ts->time_step;
 51:     th->shift      = th->Alpha_m/(th->Alpha_f*th->Gamma*ts->time_step);
 52:     TSPreStep(ts);
 53:     TSPreStage(ts,th->stage_time);
 54:     /* predictor */
 55:     VecCopy(th->X0,th->X1);
 56:     /* solve R(X,V) = 0 */
 57:     SNESSolve(ts->snes,NULL,th->X1);
 58:     /* V1 = (1-1/Gamma)*V0 + 1/(Gamma*dT)*(X1-X0) */
 59:     VecWAXPY(th->V1,-1,th->X0,th->X1);
 60:     VecAXPBY(th->V1,1-1/th->Gamma,1/(th->Gamma*ts->time_step),th->V0);
 61:     /* nonlinear solve convergence */
 62:     SNESGetConvergedReason(ts->snes,&snesreason);
 63:     if (snesreason < 0 && !th->adapt) break;
 64:     SNESGetIterationNumber(ts->snes,&its);
 65:     SNESGetLinearSolveIterations(ts->snes,&lits);
 66:     ts->snes_its += its; ts->ksp_its += lits;
 67:     PetscInfo3(ts,"step=%D, nonlinear solve iterations=%D, linear solve iterations=%D\n",ts->steps,its,lits);
 68:     /* time step adaptativity */
 69:     if (!th->adapt) break;
 70:     else {
 71:       PetscReal t1     = ts->ptime + ts->time_step;
 72:       PetscBool stepok = (reject==0) ? PETSC_TRUE : PETSC_FALSE;
 73:       th->adapt(ts,t1,th->X1,th->V1,&next_time_step,&stepok,th->adaptctx);
 74:       PetscInfo5(ts,"Step %D (t=%G,dt=%G) %s, next dt=%G\n",ts->steps,ts->ptime,ts->time_step,stepok?"accepted":"rejected",next_time_step);
 75:       if (stepok) break;
 76:     }
 77:   }
 78:   if (snesreason < 0 && ts->max_snes_failures > 0 && ++ts->num_snes_failures >= ts->max_snes_failures) {
 79:     ts->reason = TS_DIVERGED_NONLINEAR_SOLVE;
 80:     PetscInfo2(ts,"Step=%D, nonlinear solve solve failures %D greater than current TS allowed, stopping solve\n",ts->steps,ts->num_snes_failures);
 81:     return(0);
 82:   }
 83:   if (reject >= ts->max_reject) {
 84:     ts->reason = TS_DIVERGED_STEP_REJECTED;
 85:     PetscInfo2(ts,"Step=%D, step rejections %D greater than current TS allowed, stopping solve\n",ts->steps,reject);
 86:     return(0);
 87:   }
 88:   VecCopy(th->X1,ts->vec_sol);
 89:   ts->ptime    += ts->time_step;
 90:   ts->time_step = next_time_step;
 91:   ts->steps++;
 92:   return(0);
 93: }

 97: static PetscErrorCode TSInterpolate_Alpha(TS ts,PetscReal t,Vec X)
 98: {
 99:   TS_Alpha       *th = (TS_Alpha*)ts->data;
100:   PetscReal      dt  = t - ts->ptime;

104:   VecCopy(ts->vec_sol,X);
105:   VecAXPY(X,th->Gamma*dt,th->V1);
106:   VecAXPY(X,(1-th->Gamma)*dt,th->V0);
107:   return(0);
108: }

110: /*------------------------------------------------------------*/
113: static PetscErrorCode TSReset_Alpha(TS ts)
114: {
115:   TS_Alpha       *th = (TS_Alpha*)ts->data;

119:   VecDestroy(&th->X0);
120:   VecDestroy(&th->Xa);
121:   VecDestroy(&th->X1);
122:   VecDestroy(&th->V0);
123:   VecDestroy(&th->Va);
124:   VecDestroy(&th->V1);
125:   VecDestroy(&th->E);
126:   return(0);
127: }

131: static PetscErrorCode TSDestroy_Alpha(TS ts)
132: {

136:   TSReset_Alpha(ts);
137:   PetscFree(ts->data);

139:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetRadius_C",NULL);
140:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetParams_C",NULL);
141:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaGetParams_C",NULL);
142:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetAdapt_C",NULL);
143:   return(0);
144: }

148: static PetscErrorCode SNESTSFormFunction_Alpha(SNES snes,Vec x,Vec y,TS ts)
149: {
150:   TS_Alpha       *th = (TS_Alpha*)ts->data;
151:   Vec            X0  = th->X0, V0 = th->V0;
152:   Vec            X1  = x, V1 = th->V1, R = y;

156:   /* V1 = (1-1/Gamma)*V0 + 1/(Gamma*dT)*(X1-X0) */
157:   VecWAXPY(V1,-1,X0,X1);
158:   VecAXPBY(V1,1-1/th->Gamma,1/(th->Gamma*ts->time_step),V0);
159:   /* Xa = X0 + Alpha_f*(X1-X0) */
160:   VecWAXPY(th->Xa,-1,X0,X1);
161:   VecAYPX(th->Xa,th->Alpha_f,X0);
162:   /* Va = V0 + Alpha_m*(V1-V0) */
163:   VecWAXPY(th->Va,-1,V0,V1);
164:   VecAYPX(th->Va,th->Alpha_m,V0);
165:   /* F = Function(ta,Xa,Va) */
166:   TSComputeIFunction(ts,th->stage_time,th->Xa,th->Va,R,PETSC_FALSE);
167:   VecScale(R,1/th->Alpha_f);
168:   return(0);
169: }

173: static PetscErrorCode SNESTSFormJacobian_Alpha(SNES snes,Vec x,Mat *A,Mat *B,MatStructure *str,TS ts)
174: {
175:   TS_Alpha       *th = (TS_Alpha*)ts->data;

179:   /* A,B = Jacobian(ta,Xa,Va) */
180:   TSComputeIJacobian(ts,th->stage_time,th->Xa,th->Va,th->shift,A,B,str,PETSC_FALSE);
181:   return(0);
182: }

186: static PetscErrorCode TSSetUp_Alpha(TS ts)
187: {
188:   TS_Alpha       *th = (TS_Alpha*)ts->data;

192:   VecDuplicate(ts->vec_sol,&th->X0);
193:   VecDuplicate(ts->vec_sol,&th->Xa);
194:   VecDuplicate(ts->vec_sol,&th->X1);
195:   VecDuplicate(ts->vec_sol,&th->V0);
196:   VecDuplicate(ts->vec_sol,&th->Va);
197:   VecDuplicate(ts->vec_sol,&th->V1);
198:   return(0);
199: }

203: static PetscErrorCode TSSetFromOptions_Alpha(TS ts)
204: {
205:   TS_Alpha       *th = (TS_Alpha*)ts->data;

209:   PetscOptionsHead("Alpha ODE solver options");
210:   {
211:     PetscBool flag, adapt = PETSC_FALSE;
212:     PetscReal radius = 1.0;
213:     PetscOptionsReal("-ts_alpha_radius","spectral radius","TSAlphaSetRadius",radius,&radius,&flag);
214:     if (flag) { TSAlphaSetRadius(ts,radius); }
215:     PetscOptionsReal("-ts_alpha_alpha_m","algoritmic parameter alpha_m","TSAlphaSetParams",th->Alpha_m,&th->Alpha_m,NULL);
216:     PetscOptionsReal("-ts_alpha_alpha_f","algoritmic parameter alpha_f","TSAlphaSetParams",th->Alpha_f,&th->Alpha_f,NULL);
217:     PetscOptionsReal("-ts_alpha_gamma","algoritmic parameter gamma","TSAlphaSetParams",th->Gamma,&th->Gamma,NULL);
218:     TSAlphaSetParams(ts,th->Alpha_m,th->Alpha_f,th->Gamma);

220:     PetscOptionsBool("-ts_alpha_adapt","default time step adaptativity","TSAlphaSetAdapt",adapt,&adapt,&flag);
221:     if (flag) { TSAlphaSetAdapt(ts,adapt ? TSAlphaAdaptDefault : NULL,NULL); }
222:     PetscOptionsReal("-ts_alpha_adapt_rtol","relative tolerance for dt adaptativity","",th->rtol,&th->rtol,NULL);
223:     PetscOptionsReal("-ts_alpha_adapt_atol","absolute tolerance for dt adaptativity","",th->atol,&th->atol,NULL);
224:     PetscOptionsReal("-ts_alpha_adapt_min","minimum dt scale","",th->scale_min,&th->scale_min,NULL);
225:     PetscOptionsReal("-ts_alpha_adapt_max","maximum dt scale","",th->scale_max,&th->scale_max,NULL);
226:     PetscOptionsReal("-ts_alpha_adapt_dt_min","minimum dt","",th->dt_min,&th->dt_min,NULL);
227:     PetscOptionsReal("-ts_alpha_adapt_dt_max","maximum dt","",th->dt_max,&th->dt_max,NULL);
228:     SNESSetFromOptions(ts->snes);
229:   }
230:   PetscOptionsTail();
231:   return(0);
232: }

236: static PetscErrorCode TSView_Alpha(TS ts,PetscViewer viewer)
237: {
238:   TS_Alpha       *th = (TS_Alpha*)ts->data;
239:   PetscBool      iascii;

243:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
244:   if (iascii) {
245:     PetscViewerASCIIPrintf(viewer,"  Alpha_m=%G, Alpha_f=%G, Gamma=%G\n",th->Alpha_m,th->Alpha_f,th->Gamma);
246:   }
247:   SNESView(ts->snes,viewer);
248:   return(0);
249: }

251: /*------------------------------------------------------------*/

255: PetscErrorCode  TSAlphaSetRadius_Alpha(TS ts,PetscReal radius)
256: {
257:   TS_Alpha *th = (TS_Alpha*)ts->data;

260:   if (radius < 0 || radius > 1) SETERRQ1(PetscObjectComm((PetscObject)ts),PETSC_ERR_ARG_OUTOFRANGE,"Radius %G not in range [0,1]",radius);
261:   th->Alpha_m = 0.5*(3-radius)/(1+radius);
262:   th->Alpha_f = 1/(1+radius);
263:   th->Gamma   = 0.5 + th->Alpha_m - th->Alpha_f;
264:   return(0);
265: }

269: PetscErrorCode  TSAlphaSetParams_Alpha(TS ts,PetscReal alpha_m,PetscReal alpha_f,PetscReal gamma)
270: {
271:   TS_Alpha *th = (TS_Alpha*)ts->data;

274:   th->Alpha_m = alpha_m;
275:   th->Alpha_f = alpha_f;
276:   th->Gamma   = gamma;
277:   return(0);
278: }

282: PetscErrorCode  TSAlphaGetParams_Alpha(TS ts,PetscReal *alpha_m,PetscReal *alpha_f,PetscReal *gamma)
283: {
284:   TS_Alpha *th = (TS_Alpha*)ts->data;

287:   if (alpha_m) *alpha_m = th->Alpha_m;
288:   if (alpha_f) *alpha_f = th->Alpha_f;
289:   if (gamma)   *gamma   = th->Gamma;
290:   return(0);
291: }

295: PetscErrorCode  TSAlphaSetAdapt_Alpha(TS ts,TSAlphaAdaptFunction adapt,void *ctx)
296: {
297:   TS_Alpha *th = (TS_Alpha*)ts->data;

300:   th->adapt    = adapt;
301:   th->adaptctx = ctx;
302:   return(0);
303: }

305: /* ------------------------------------------------------------ */
306: /*MC
307:       TSALPHA - DAE solver using the implicit Generalized-Alpha method

309:   Level: beginner

311:   References:
312:   K.E. Jansen, C.H. Whiting, G.M. Hulber, "A generalized-alpha
313:   method for integrating the filtered Navier-Stokes equations with a
314:   stabilized finite element method", Computer Methods in Applied
315:   Mechanics and Engineering, 190, 305-319, 2000.
316:   DOI: 10.1016/S0045-7825(00)00203-6.

318:   J. Chung, G.M.Hubert. "A Time Integration Algorithm for Structural
319:   Dynamics with Improved Numerical Dissipation: The Generalized-alpha
320:   Method" ASME Journal of Applied Mechanics, 60, 371:375, 1993.

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

324: M*/
327: PETSC_EXTERN PetscErrorCode TSCreate_Alpha(TS ts)
328: {
329:   TS_Alpha       *th;

333:   ts->ops->reset          = TSReset_Alpha;
334:   ts->ops->destroy        = TSDestroy_Alpha;
335:   ts->ops->view           = TSView_Alpha;
336:   ts->ops->setup          = TSSetUp_Alpha;
337:   ts->ops->step           = TSStep_Alpha;
338:   ts->ops->interpolate    = TSInterpolate_Alpha;
339:   ts->ops->setfromoptions = TSSetFromOptions_Alpha;
340:   ts->ops->snesfunction   = SNESTSFormFunction_Alpha;
341:   ts->ops->snesjacobian   = SNESTSFormJacobian_Alpha;

343:   PetscNewLog(ts,TS_Alpha,&th);
344:   ts->data = (void*)th;

346:   th->Alpha_m = 0.5;
347:   th->Alpha_f = 0.5;
348:   th->Gamma   = 0.5;

350:   th->rtol      = 1e-3;
351:   th->atol      = 1e-3;
352:   th->rho       = 0.9;
353:   th->scale_min = 0.1;
354:   th->scale_max = 5.0;
355:   th->dt_min    = 0.0;
356:   th->dt_max    = PETSC_MAX_REAL;

358:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetAdapt_C",TSAlphaSetAdapt_Alpha);
359:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetRadius_C",TSAlphaSetRadius_Alpha);
360:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaSetParams_C",TSAlphaSetParams_Alpha);
361:   PetscObjectComposeFunction((PetscObject)ts,"TSAlphaGetParams_C",TSAlphaGetParams_Alpha);
362:   return(0);
363: }

367: /*@C
368:   TSAlphaSetAdapt - sets the time step adaptativity and acceptance test routine

370:   This function allows to accept/reject a step and select the
371:   next time step to use.

373:   Not Collective

375:   Input Parameter:
376: +  ts - timestepping context
377: .  adapt - user-defined adapt routine
378: -  ctx  - [optional] user-defined context for private data for the
379:          adapt routine (may be NULL)

381:    Calling sequence of adapt:
382: $    adapt (TS ts,PetscReal t,Vec X,Vec Xdot,
383: $            PetscReal *next_dt,PetscBool *accepted,void *ctx);

385:   Level: intermediate

387: @*/
388: PetscErrorCode  TSAlphaSetAdapt(TS ts,TSAlphaAdaptFunction adapt,void *ctx)
389: {

394:   PetscTryMethod(ts,"TSAlphaSetAdapt_C",(TS,TSAlphaAdaptFunction,void*),(ts,adapt,ctx));
395:   return(0);
396: }

400: PetscErrorCode  TSAlphaAdaptDefault(TS ts,PetscReal t,Vec X,Vec Xdot, PetscReal *nextdt,PetscBool *ok,void *ctx)
401: {
402:   TS_Alpha            *th;
403:   SNESConvergedReason snesreason;
404:   PetscReal           dt,normX,normE,Emax,scale;
405:   PetscErrorCode      ierr;

409: #if PETSC_USE_DEBUG
410:   {
411:     PetscBool match;
412:     PetscObjectTypeCompare((PetscObject)ts,TSALPHA,&match);
413:     if (!match) SETERRQ(PetscObjectComm((PetscObject)ts),1,"Only for TSALPHA");
414:   }
415: #endif
416:   th = (TS_Alpha*)ts->data;

418:   SNESGetConvergedReason(ts->snes,&snesreason);
419:   if (snesreason < 0) {
420:     *ok      = PETSC_FALSE;
421:     *nextdt *= th->scale_min;
422:     goto finally;
423:   }

425:   /* first-order aproximation to the local error */
426:   /* E = (X0 + dt*Xdot) - X */
427:   TSGetTimeStep(ts,&dt);
428:   if (!th->E) {VecDuplicate(th->X0,&th->E);}
429:   VecWAXPY(th->E,dt,Xdot,th->X0);
430:   VecAXPY(th->E,-1,X);
431:   VecNorm(th->E,NORM_2,&normE);
432:   /* compute maximum allowable error */
433:   VecNorm(X,NORM_2,&normX);
434:   if (normX == 0) {VecNorm(th->X0,NORM_2,&normX);}
435:   Emax =  th->rtol * normX + th->atol;
436:   /* compute next time step */
437:   if (normE > 0) {
438:     scale = th->rho * PetscRealPart(PetscSqrtScalar((PetscScalar)(Emax/normE)));
439:     scale = PetscMax(scale,th->scale_min);
440:     scale = PetscMin(scale,th->scale_max);
441:     if (!(*ok)) scale = PetscMin(1.0,scale);
442:     *nextdt *= scale;
443:   }
444:   /* accept or reject step */
445:   if (normE <= Emax) *ok = PETSC_TRUE;
446:   else               *ok = PETSC_FALSE;

448: finally:
449:   *nextdt = PetscMax(*nextdt,th->dt_min);
450:   *nextdt = PetscMin(*nextdt,th->dt_max);
451:   return(0);
452: }

456: /*@
457:   TSAlphaSetRadius - sets the desired spectral radius of the method
458:                      (i.e. high-frequency numerical damping)

460:   Logically Collective on TS

462:   The algorithmic parameters \alpha_m and \alpha_f of the
463:   generalized-\alpha method can be computed in terms of a specified
464:   spectral radius \rho in [0,1] for infinite time step in order to
465:   control high-frequency numerical damping:
466:     alpha_m = 0.5*(3-\rho)/(1+\rho)
467:     alpha_f = 1/(1+\rho)

469:   Input Parameter:
470: +  ts - timestepping context
471: -  radius - the desired spectral radius

473:   Options Database:
474: .  -ts_alpha_radius <radius>

476:   Level: intermediate

478: .seealso: TSAlphaSetParams(), TSAlphaGetParams()
479: @*/
480: PetscErrorCode  TSAlphaSetRadius(TS ts,PetscReal radius)
481: {

486:   PetscTryMethod(ts,"TSAlphaSetRadius_C",(TS,PetscReal),(ts,radius));
487:   return(0);
488: }

492: /*@
493:   TSAlphaSetParams - sets the algorithmic parameters for TSALPHA

495:   Not Collective

497:   Second-order accuracy can be obtained so long as:
498:     \gamma = 0.5 + alpha_m - alpha_f

500:   Unconditional stability requires:
501:     \alpha_m >= \alpha_f >= 0.5

503:   Backward Euler method is recovered when:
504:     \alpha_m = \alpha_f = gamma = 1


507:   Input Parameter:
508: +  ts - timestepping context
509: .  \alpha_m - algorithmic paramenter
510: .  \alpha_f - algorithmic paramenter
511: -  \gamma   - algorithmic paramenter

513:    Options Database:
514: +  -ts_alpha_alpha_m <alpha_m>
515: .  -ts_alpha_alpha_f <alpha_f>
516: -  -ts_alpha_gamma <gamma>

518:   Note:
519:   Use of this function is normally only required to hack TSALPHA to
520:   use a modified integration scheme. Users should call
521:   TSAlphaSetRadius() to set the desired spectral radius of the methods
522:   (i.e. high-frequency damping) in order so select optimal values for
523:   these parameters.

525:   Level: advanced

527: .seealso: TSAlphaSetRadius(), TSAlphaGetParams()
528: @*/
529: PetscErrorCode  TSAlphaSetParams(TS ts,PetscReal alpha_m,PetscReal alpha_f,PetscReal gamma)
530: {

535:   PetscTryMethod(ts,"TSAlphaSetParams_C",(TS,PetscReal,PetscReal,PetscReal),(ts,alpha_m,alpha_f,gamma));
536:   return(0);
537: }

541: /*@
542:   TSAlphaGetParams - gets the algorithmic parameters for TSALPHA

544:   Not Collective

546:   Input Parameter:
547: +  ts - timestepping context
548: .  \alpha_m - algorithmic parameter
549: .  \alpha_f - algorithmic parameter
550: -  \gamma   - algorithmic parameter

552:   Note:
553:   Use of this function is normally only required to hack TSALPHA to
554:   use a modified integration scheme. Users should call
555:   TSAlphaSetRadius() to set the high-frequency damping (i.e. spectral
556:   radius of the method) in order so select optimal values for these
557:   parameters.

559:   Level: advanced

561: .seealso: TSAlphaSetRadius(), TSAlphaSetParams()
562: @*/
563: PetscErrorCode  TSAlphaGetParams(TS ts,PetscReal *alpha_m,PetscReal *alpha_f,PetscReal *gamma)
564: {

572:   PetscUseMethod(ts,"TSAlphaGetParams_C",(TS,PetscReal*,PetscReal*,PetscReal*),(ts,alpha_m,alpha_f,gamma));
573:   return(0);
574: }