Date: 2013-07-02T14:51:11+00:00

Actual source code: posindep.c
petsc-3.4.2 2013-07-02

      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: }