Actual source code: mrk.c
petsc-3.13.6 2020-09-29
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      1: /*
      2:   Code for time stepping with the multi-rate Runge-Kutta method

      4:   Notes:
      5:   1) The general system is written as
      6:      Udot = F(t,U) for the nonsplit version of multi-rate RK,
      7:      user should give the indexes for both slow and fast components;
      8:   2) The general system is written as
      9:      Usdot = Fs(t,Us,Uf)
     10:      Ufdot = Ff(t,Us,Uf) for multi-rate RK with RHS splits,
     11:      user should partioned RHS by themselves and also provide the indexes for both slow and fast components.
     12: */

     14:  #include <petsc/private/tsimpl.h>
     15:  #include <petscdm.h>
     16:  #include <../src/ts/impls/explicit/rk/rk.h>
     17:  #include <../src/ts/impls/explicit/rk/mrk.h>

     19: static PetscErrorCode TSReset_RK_MultirateNonsplit(TS ts)
     20: {
     21:   TS_RK          *rk = (TS_RK*)ts->data;
     22:   RKTableau      tab = rk->tableau;

     26:   VecDestroy(&rk->X0);
     27:   VecDestroyVecs(tab->s,&rk->YdotRHS_slow);
     28:   return(0);
     29: }

     31: static PetscErrorCode TSInterpolate_RK_MultirateNonsplit(TS ts,PetscReal itime,Vec X)
     32: {
     33:   TS_RK            *rk = (TS_RK*)ts->data;
     34:   PetscInt         s = rk->tableau->s,p = rk->tableau->p,i,j;
     35:   PetscReal        h = ts->time_step;
     36:   PetscReal        tt,t;
     37:   PetscScalar      *b;
     38:   const PetscReal  *B = rk->tableau->binterp;
     39:   PetscErrorCode   ierr;

     42:   if (!B) SETERRQ1(PetscObjectComm((PetscObject)ts),PETSC_ERR_SUP,"TSRK %s does not have an interpolation formula",rk->tableau->name);
     43:   t = (itime - rk->ptime)/h;
     44:   PetscMalloc1(s,&b);
     45:   for (i=0; i<s; i++) b[i] = 0;
     46:   for (j=0,tt=t; j<p; j++,tt*=t) {
     47:     for (i=0; i<s; i++) {
     48:       b[i]  += h * B[i*p+j] * tt;
     49:     }
     50:   }
     51:   VecCopy(rk->X0,X);
     52:   VecMAXPY(X,s,b,rk->YdotRHS_slow);
     53:   PetscFree(b);
     54:   return(0);
     55: }

     57: static PetscErrorCode TSStepRefine_RK_MultirateNonsplit(TS ts)
     58: {
     59:   TS              previousts,subts;
     60:   TS_RK           *rk = (TS_RK*)ts->data;
     61:   RKTableau       tab = rk->tableau;
     62:   Vec             *Y = rk->Y,*YdotRHS = rk->YdotRHS;
     63:   Vec             vec_fast,subvec_fast;
     64:   const PetscInt  s = tab->s;
     65:   const PetscReal *A = tab->A,*c = tab->c;
     66:   PetscScalar     *w = rk->work;
     67:   PetscInt        i,j,k;
     68:   PetscReal       t = ts->ptime,h = ts->time_step;
     69:   PetscErrorCode  ierr;

     71:   VecDuplicate(ts->vec_sol,&vec_fast);
     72:   previousts = rk->subts_current;
     73:   TSRHSSplitGetSubTS(rk->subts_current,"fast",&subts);
     74:   TSRHSSplitGetSubTS(subts,"fast",&subts);
     75:   for (k=0; k<rk->dtratio; k++) {
     76:     for (i=0; i<s; i++) {
     77:       TSInterpolate_RK_MultirateNonsplit(ts,t+k*h/rk->dtratio+h/rk->dtratio*c[i],Y[i]);
     78:       for (j=0; j<i; j++) w[j] = h/rk->dtratio*A[i*s+j];
     79:       /* update the fast components in the stage value, the slow components will be ignored, so we do not care the slow part in vec_fast */
     80:       VecCopy(ts->vec_sol,vec_fast);
     81:       VecMAXPY(vec_fast,i,w,YdotRHS);
     82:       /* update the fast components in the stage value */
     83:       VecGetSubVector(vec_fast,rk->is_fast,&subvec_fast);
     84:       VecISCopy(Y[i],rk->is_fast,SCATTER_FORWARD,subvec_fast);
     85:       VecRestoreSubVector(vec_fast,rk->is_fast,&subvec_fast);
     86:       /* compute the stage RHS */
     87:       TSComputeRHSFunction(ts,t+k*h/rk->dtratio+h/rk->dtratio*c[i],Y[i],YdotRHS[i]);
     88:     }
     89:     VecCopy(ts->vec_sol,vec_fast);
     90:     TSEvaluateStep(ts,tab->order,vec_fast,NULL);
     91:     /* update the fast components in the solution */
     92:     VecGetSubVector(vec_fast,rk->is_fast,&subvec_fast);
     93:     VecISCopy(ts->vec_sol,rk->is_fast,SCATTER_FORWARD,subvec_fast);
     94:     VecRestoreSubVector(vec_fast,rk->is_fast,&subvec_fast);

     96:     if (subts) {
     97:       Vec *YdotRHS_copy;
     98:       VecDuplicateVecs(ts->vec_sol,s,&YdotRHS_copy);
     99:       rk->subts_current = rk->subts_fast;
    100:       ts->ptime = t+k*h/rk->dtratio;
    101:       ts->time_step = h/rk->dtratio;
    102:       TSRHSSplitGetIS(rk->subts_current,"fast",&rk->is_fast);
    103:       for (i=0; i<s; i++) {
    104:         VecCopy(rk->YdotRHS_slow[i],YdotRHS_copy[i]);
    105:         VecCopy(YdotRHS[i],rk->YdotRHS_slow[i]);
    106:       }

    108:       TSStepRefine_RK_MultirateNonsplit(ts);

    110:       rk->subts_current = previousts;
    111:       ts->ptime = t;
    112:       ts->time_step = h;
    113:       TSRHSSplitGetIS(previousts,"fast",&rk->is_fast);
    114:       for (i=0; i<s; i++) {
    115:         VecCopy(YdotRHS_copy[i],rk->YdotRHS_slow[i]);
    116:       }
    117:       VecDestroyVecs(s,&YdotRHS_copy);
    118:     }
    119:   }
    120:   VecDestroy(&vec_fast);
    121:   return(0);
    122: }

    124: static PetscErrorCode TSStep_RK_MultirateNonsplit(TS ts)
    125: {
    126:   TS_RK           *rk = (TS_RK*)ts->data;
    127:   RKTableau       tab = rk->tableau;
    128:   Vec             *Y = rk->Y,*YdotRHS = rk->YdotRHS,*YdotRHS_slow = rk->YdotRHS_slow;
    129:   Vec             stage_slow,sol_slow; /* vectors store the slow components */
    130:   Vec             subvec_slow; /* sub vector to store the slow components */
    131:   IS              is_slow = rk->is_slow;
    132:   const PetscInt  s = tab->s;
    133:   const PetscReal *A = tab->A,*c = tab->c;
    134:   PetscScalar     *w = rk->work;
    135:   PetscInt        i,j,dtratio = rk->dtratio;
    136:   PetscReal       next_time_step = ts->time_step,t = ts->ptime,h = ts->time_step;
    137:   PetscErrorCode  ierr;

    140:   rk->status = TS_STEP_INCOMPLETE;
    141:   VecDuplicate(ts->vec_sol,&stage_slow);
    142:   VecDuplicate(ts->vec_sol,&sol_slow);
    143:   VecCopy(ts->vec_sol,rk->X0);
    144:   for (i=0; i<s; i++) {
    145:     rk->stage_time = t + h*c[i];
    146:     TSPreStage(ts,rk->stage_time);
    147:     VecCopy(ts->vec_sol,Y[i]);
    148:     for (j=0; j<i; j++) w[j] = h*A[i*s+j];
    149:     VecMAXPY(Y[i],i,w,YdotRHS_slow);
    150:     TSPostStage(ts,rk->stage_time,i,Y);
    151:     /* compute the stage RHS */
    152:     TSComputeRHSFunction(ts,t+h*c[i],Y[i],YdotRHS_slow[i]);
    153:   }
    154:   /* update the slow components in the solution */
    155:   rk->YdotRHS = YdotRHS_slow;
    156:   rk->dtratio = 1;
    157:   TSEvaluateStep(ts,tab->order,sol_slow,NULL);
    158:   rk->dtratio = dtratio;
    159:   rk->YdotRHS = YdotRHS;
    160:   /* update the slow components in the solution */
    161:   VecGetSubVector(sol_slow,is_slow,&subvec_slow);
    162:   VecISCopy(ts->vec_sol,is_slow,SCATTER_FORWARD,subvec_slow);
    163:   VecRestoreSubVector(sol_slow,is_slow,&subvec_slow);

    165:   rk->subts_current = ts;
    166:   rk->ptime = t;
    167:   rk->time_step = h;
    168:   TSStepRefine_RK_MultirateNonsplit(ts);

    170:   ts->ptime = t + ts->time_step;
    171:   ts->time_step = next_time_step;
    172:   rk->status = TS_STEP_COMPLETE;

    174:   /* free memory of work vectors */
    175:   VecDestroy(&stage_slow);
    176:   VecDestroy(&sol_slow);
    177:   return(0);
    178: }

    180: static PetscErrorCode TSSetUp_RK_MultirateNonsplit(TS ts)
    181: {
    182:   TS_RK          *rk = (TS_RK*)ts->data;
    183:   RKTableau      tab = rk->tableau;

    187:   TSRHSSplitGetIS(ts,"slow",&rk->is_slow);
    188:   TSRHSSplitGetIS(ts,"fast",&rk->is_fast);
    189:   if (!rk->is_slow || !rk->is_fast) SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_USER,"Must set up RHSSplits with TSRHSSplitSetIS() using split names 'slow' and 'fast' respectively in order to use multirate RK");
    190:   TSRHSSplitGetSubTS(ts,"slow",&rk->subts_slow);
    191:   TSRHSSplitGetSubTS(ts,"fast",&rk->subts_fast);
    192:   if (!rk->subts_slow || !rk->subts_fast) SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_USER,"Must set up the RHSFunctions for 'slow' and 'fast' components using TSRHSSplitSetRHSFunction() or calling TSSetRHSFunction() for each sub-TS");
    193:   VecDuplicate(ts->vec_sol,&rk->X0);
    194:   VecDuplicateVecs(ts->vec_sol,tab->s,&rk->YdotRHS_slow);
    195:   rk->subts_current = rk->subts_fast;

    197:   ts->ops->step        = TSStep_RK_MultirateNonsplit;
    198:   ts->ops->interpolate = TSInterpolate_RK_MultirateNonsplit;
    199:   return(0);
    200: }

    202: /*
    203:   Copy DM from tssrc to tsdest, while keeping the original DMTS and DMSNES in tsdest.
    204: */
    205: static PetscErrorCode TSCopyDM(TS tssrc,TS tsdest)
    206: {
    207:   DM             newdm,dmsrc,dmdest;

    211:   TSGetDM(tssrc,&dmsrc);
    212:   DMClone(dmsrc,&newdm);
    213:   TSGetDM(tsdest,&dmdest);
    214:   DMCopyDMTS(dmdest,newdm);
    215:   DMCopyDMSNES(dmdest,newdm);
    216:   TSSetDM(tsdest,newdm);
    217:   DMDestroy(&newdm);
    218:   return(0);
    219: }

    221: static PetscErrorCode TSReset_RK_MultirateSplit(TS ts)
    222: {
    223:   TS_RK          *rk = (TS_RK*)ts->data;

    227:   if (rk->subts_slow) {
    228:     PetscFree(rk->subts_slow->data);
    229:     rk->subts_slow = NULL;
    230:   }
    231:   if (rk->subts_fast) {
    232:     PetscFree(rk->YdotRHS_fast);
    233:     PetscFree(rk->YdotRHS_slow);
    234:     VecDestroy(&rk->X0);
    235:     TSReset_RK_MultirateSplit(rk->subts_fast);
    236:     PetscFree(rk->subts_fast->data);
    237:     rk->subts_fast = NULL;
    238:   }
    239:   return(0);
    240: }

    242: static PetscErrorCode TSInterpolate_RK_MultirateSplit(TS ts,PetscReal itime,Vec X)
    243: {
    244:   TS_RK           *rk = (TS_RK*)ts->data;
    245:   Vec             Xslow;
    246:   PetscInt        s = rk->tableau->s,p = rk->tableau->p,i,j;
    247:   PetscReal       h;
    248:   PetscReal       tt,t;
    249:   PetscScalar     *b;
    250:   const PetscReal *B = rk->tableau->binterp;
    251:   PetscErrorCode  ierr;

    254:   if (!B) SETERRQ1(PetscObjectComm((PetscObject)ts),PETSC_ERR_SUP,"TSRK %s does not have an interpolation formula",rk->tableau->name);

    256:   switch (rk->status) {
    257:     case TS_STEP_INCOMPLETE:
    258:     case TS_STEP_PENDING:
    259:       h = ts->time_step;
    260:       t = (itime - ts->ptime)/h;
    261:       break;
    262:     case TS_STEP_COMPLETE:
    263:       h = ts->ptime - ts->ptime_prev;
    264:       t = (itime - ts->ptime)/h + 1; /* In the interval [0,1] */
    265:       break;
    266:     default: SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_PLIB,"Invalid TSStepStatus");
    267:   }
    268:   PetscMalloc1(s,&b);
    269:   for (i=0; i<s; i++) b[i] = 0;
    270:   for (j=0,tt=t; j<p; j++,tt*=t) {
    271:     for (i=0; i<s; i++) {
    272:       b[i]  += h * B[i*p+j] * tt;
    273:     }
    274:   }
    275:   for (i=0; i<s; i++) {
    276:     VecGetSubVector(rk->YdotRHS[i],rk->is_slow,&rk->YdotRHS_slow[i]);
    277:   }
    278:   VecGetSubVector(X,rk->is_slow,&Xslow);
    279:   VecISCopy(rk->X0,rk->is_slow,SCATTER_REVERSE,Xslow);
    280:   VecMAXPY(Xslow,s,b,rk->YdotRHS_slow);
    281:   VecRestoreSubVector(X,rk->is_slow,&Xslow);
    282:   for (i=0; i<s; i++) {
    283:     VecRestoreSubVector(rk->YdotRHS[i],rk->is_slow,&rk->YdotRHS_slow[i]);
    284:   }
    285:   PetscFree(b);
    286:   return(0);
    287: }

    289: /*
    290:  This is for partitioned RHS multirate RK method
    291:  The step completion formula is

    293:  x1 = x0 + h b^T YdotRHS

    295: */
    296: static PetscErrorCode TSEvaluateStep_RK_MultirateSplit(TS ts,PetscInt order,Vec X,PetscBool *done)
    297: {
    298:   TS_RK          *rk = (TS_RK*)ts->data;
    299:   RKTableau      tab = rk->tableau;
    300:   Vec            Xslow,Xfast;                  /* subvectors of X which store slow components and fast components respectively */
    301:   PetscScalar    *w = rk->work;
    302:   PetscReal      h = ts->time_step;
    303:   PetscInt       s = tab->s,j;

    307:   VecCopy(ts->vec_sol,X);
    308:   if (rk->slow) {
    309:     for (j=0; j<s; j++) w[j] = h*tab->b[j];
    310:     VecGetSubVector(ts->vec_sol,rk->is_slow,&Xslow);
    311:     VecMAXPY(Xslow,s,w,rk->YdotRHS_slow);
    312:     VecRestoreSubVector(ts->vec_sol,rk->is_slow,&Xslow);
    313:   } else {
    314:     for (j=0; j<s; j++) w[j] = h/rk->dtratio*tab->b[j];
    315:     VecGetSubVector(X,rk->is_fast,&Xfast);
    316:     VecMAXPY(Xfast,s,w,rk->YdotRHS_fast);
    317:     VecRestoreSubVector(X,rk->is_fast,&Xfast);
    318:   }
    319:   return(0);
    320: }

    322: static PetscErrorCode TSStepRefine_RK_MultirateSplit(TS ts)
    323: {
    324:   TS_RK           *rk = (TS_RK*)ts->data;
    325:   TS              subts_fast = rk->subts_fast,currentlevelts;
    326:   TS_RK           *subrk_fast = (TS_RK*)subts_fast->data;
    327:   RKTableau       tab = rk->tableau;
    328:   Vec             *Y = rk->Y;
    329:   Vec             *YdotRHS = rk->YdotRHS,*YdotRHS_fast = rk->YdotRHS_fast;
    330:   Vec             Yfast,Xfast;
    331:   const PetscInt  s = tab->s;
    332:   const PetscReal *A = tab->A,*c = tab->c;
    333:   PetscScalar     *w = rk->work;
    334:   PetscInt        i,j,k;
    335:   PetscReal       t = ts->ptime,h = ts->time_step;
    336:   PetscErrorCode  ierr;

    338:   for (k=0; k<rk->dtratio; k++) {
    339:     VecGetSubVector(ts->vec_sol,rk->is_fast,&Xfast);
    340:     for (i=0; i<s; i++) {
    341:       VecGetSubVector(YdotRHS[i],rk->is_fast,&YdotRHS_fast[i]);
    342:     }
    343:     /* propogate fast component using small time steps */
    344:     for (i=0; i<s; i++) {
    345:       /* stage value for slow components */
    346:       TSInterpolate_RK_MultirateSplit(rk->ts_root,t+k*h/rk->dtratio+h/rk->dtratio*c[i],Y[i]);
    347:       currentlevelts = rk->ts_root;
    348:       while (currentlevelts != ts) { /* all the slow parts need to be interpolated separated */
    349:         currentlevelts = ((TS_RK*)currentlevelts->data)->subts_fast;
    350:         TSInterpolate_RK_MultirateSplit(currentlevelts,t+k*h/rk->dtratio+h/rk->dtratio*c[i],Y[i]);
    351:       }
    352:       for (j=0; j<i; j++) w[j] = h/rk->dtratio*A[i*s+j];
    353:       subrk_fast->stage_time = t + h/rk->dtratio*c[i];
    354:       TSPreStage(subts_fast,subrk_fast->stage_time);
    355:       /* stage value for fast components */
    356:       VecGetSubVector(Y[i],rk->is_fast,&Yfast);
    357:       VecCopy(Xfast,Yfast);
    358:       VecMAXPY(Yfast,i,w,YdotRHS_fast);
    359:       VecRestoreSubVector(Y[i],rk->is_fast,&Yfast);
    360:       TSPostStage(subts_fast,subrk_fast->stage_time,i,Y);
    361:       /* compute the stage RHS for fast components */
    362:       TSComputeRHSFunction(subts_fast,t+k*h*rk->dtratio+h/rk->dtratio*c[i],Y[i],YdotRHS_fast[i]);
    363:     }
    364:     VecRestoreSubVector(ts->vec_sol,rk->is_fast,&Xfast);
    365:     /* update the value of fast components using fast time step */
    366:     rk->slow = PETSC_FALSE;
    367:     TSEvaluateStep_RK_MultirateSplit(ts,tab->order,ts->vec_sol,NULL);
    368:     for (i=0; i<s; i++) {
    369:       VecRestoreSubVector(YdotRHS[i],rk->is_fast,&YdotRHS_fast[i]);
    370:     }

    372:     if (subrk_fast->subts_fast) {
    373:       subts_fast->ptime = t+k*h/rk->dtratio;
    374:       subts_fast->time_step = h/rk->dtratio;
    375:       TSStepRefine_RK_MultirateSplit(subts_fast);
    376:     }
    377:     /* update the fast components of the solution */
    378:     VecGetSubVector(ts->vec_sol,rk->is_fast,&Xfast);
    379:     VecISCopy(rk->X0,rk->is_fast,SCATTER_FORWARD,Xfast);
    380:     VecRestoreSubVector(ts->vec_sol,rk->is_fast,&Xfast);
    381:   }
    382:   return(0);
    383: }

    385: static PetscErrorCode TSStep_RK_MultirateSplit(TS ts)
    386: {
    387:   TS_RK           *rk = (TS_RK*)ts->data;
    388:   RKTableau       tab = rk->tableau;
    389:   Vec             *Y = rk->Y,*YdotRHS = rk->YdotRHS;
    390:   Vec             *YdotRHS_fast = rk->YdotRHS_fast,*YdotRHS_slow = rk->YdotRHS_slow;
    391:   Vec             Yslow,Yfast; /* subvectors store the stges of slow components and fast components respectively                           */
    392:   const PetscInt  s = tab->s;
    393:   const PetscReal *A = tab->A,*c = tab->c;
    394:   PetscScalar     *w = rk->work;
    395:   PetscInt        i,j;
    396:   PetscReal       next_time_step = ts->time_step,t = ts->ptime,h = ts->time_step;
    397:   PetscErrorCode  ierr;

    400:   rk->status = TS_STEP_INCOMPLETE;
    401:   for (i=0; i<s; i++) {
    402:     VecGetSubVector(YdotRHS[i],rk->is_slow,&YdotRHS_slow[i]);
    403:     VecGetSubVector(YdotRHS[i],rk->is_fast,&YdotRHS_fast[i]);
    404:   }
    405:   VecCopy(ts->vec_sol,rk->X0);
    406:   /* propogate both slow and fast components using large time steps */
    407:   for (i=0; i<s; i++) {
    408:     rk->stage_time = t + h*c[i];
    409:     TSPreStage(ts,rk->stage_time);
    410:     VecCopy(ts->vec_sol,Y[i]);
    411:     VecGetSubVector(Y[i],rk->is_fast,&Yfast);
    412:     VecGetSubVector(Y[i],rk->is_slow,&Yslow);
    413:     for (j=0; j<i; j++) w[j] = h*A[i*s+j];
    414:     VecMAXPY(Yfast,i,w,YdotRHS_fast);
    415:     VecMAXPY(Yslow,i,w,YdotRHS_slow);
    416:     VecRestoreSubVector(Y[i],rk->is_fast,&Yfast);
    417:     VecRestoreSubVector(Y[i],rk->is_slow,&Yslow);
    418:     TSPostStage(ts,rk->stage_time,i,Y);
    419:     TSComputeRHSFunction(rk->subts_slow,t+h*c[i],Y[i],YdotRHS_slow[i]);
    420:     TSComputeRHSFunction(rk->subts_fast,t+h*c[i],Y[i],YdotRHS_fast[i]);
    421:   }
    422:   rk->slow = PETSC_TRUE;
    423:   /* update the slow components of the solution using slow time step */
    424:   TSEvaluateStep_RK_MultirateSplit(ts,tab->order,ts->vec_sol,NULL);
    425:   /* YdotRHS will be used for interpolation during refinement */
    426:   for (i=0; i<s; i++) {
    427:     VecRestoreSubVector(YdotRHS[i],rk->is_slow,&YdotRHS_slow[i]);
    428:     VecRestoreSubVector(YdotRHS[i],rk->is_fast,&YdotRHS_fast[i]);
    429:   }

    431:   TSStepRefine_RK_MultirateSplit(ts);

    433:   ts->ptime = t + ts->time_step;
    434:   ts->time_step = next_time_step;
    435:   rk->status = TS_STEP_COMPLETE;
    436:   return(0);
    437: }

    439: static PetscErrorCode TSSetUp_RK_MultirateSplit(TS ts)
    440: {
    441:   TS_RK          *rk = (TS_RK*)ts->data,*nextlevelrk,*currentlevelrk;
    442:   TS             nextlevelts;
    443:   Vec            X0;

    447:   TSRHSSplitGetIS(ts,"slow",&rk->is_slow);
    448:   TSRHSSplitGetIS(ts,"fast",&rk->is_fast);
    449:   if (!rk->is_slow || !rk->is_fast) SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_USER,"Must set up RHSSplits with TSRHSSplitSetIS() using split names 'slow' and 'fast' respectively in order to use -ts_type bsi");
    450:   TSRHSSplitGetSubTS(ts,"slow",&rk->subts_slow);
    451:   TSRHSSplitGetSubTS(ts,"fast",&rk->subts_fast);
    452:   if (!rk->subts_slow || !rk->subts_fast) SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_USER,"Must set up the RHSFunctions for 'slow' and 'fast' components using TSRHSSplitSetRHSFunction() or calling TSSetRHSFunction() for each sub-TS");

    454:   VecDuplicate(ts->vec_sol,&X0);
    455:   /* The TS at each level share the same tableau, work array, solution vector, stage values and stage derivatives */
    456:   currentlevelrk = rk;
    457:   while (currentlevelrk->subts_fast) {
    458:     PetscMalloc1(rk->tableau->s,&currentlevelrk->YdotRHS_fast);
    459:     PetscMalloc1(rk->tableau->s,&currentlevelrk->YdotRHS_slow);
    460:     PetscObjectReference((PetscObject)X0);
    461:     currentlevelrk->X0 = X0;
    462:     currentlevelrk->ts_root = ts;

    464:     /* set up the ts for the slow part */
    465:     nextlevelts = currentlevelrk->subts_slow;
    466:     PetscNewLog(nextlevelts,&nextlevelrk);
    467:     nextlevelrk->tableau = rk->tableau;
    468:     nextlevelrk->work = rk->work;
    469:     nextlevelrk->Y = rk->Y;
    470:     nextlevelrk->YdotRHS = rk->YdotRHS;
    471:     nextlevelts->data = (void*)nextlevelrk;
    472:     TSCopyDM(ts,nextlevelts);
    473:     TSSetSolution(nextlevelts,ts->vec_sol);

    475:     /* set up the ts for the fast part */
    476:     nextlevelts = currentlevelrk->subts_fast;
    477:     PetscNewLog(nextlevelts,&nextlevelrk);
    478:     nextlevelrk->tableau = rk->tableau;
    479:     nextlevelrk->work = rk->work;
    480:     nextlevelrk->Y = rk->Y;
    481:     nextlevelrk->YdotRHS = rk->YdotRHS;
    482:     nextlevelrk->dtratio = rk->dtratio;
    483:     TSRHSSplitGetIS(nextlevelts,"slow",&nextlevelrk->is_slow);
    484:     TSRHSSplitGetSubTS(nextlevelts,"slow",&nextlevelrk->subts_slow);
    485:     TSRHSSplitGetIS(nextlevelts,"fast",&nextlevelrk->is_fast);
    486:     TSRHSSplitGetSubTS(nextlevelts,"fast",&nextlevelrk->subts_fast);
    487:     nextlevelts->data = (void*)nextlevelrk;
    488:     TSCopyDM(ts,nextlevelts);
    489:     TSSetSolution(nextlevelts,ts->vec_sol);

    491:     currentlevelrk = nextlevelrk;
    492:   }
    493:   VecDestroy(&X0);

    495:   ts->ops->step         = TSStep_RK_MultirateSplit;
    496:   ts->ops->evaluatestep = TSEvaluateStep_RK_MultirateSplit;
    497:   ts->ops->interpolate  = TSInterpolate_RK_MultirateSplit;
    498:   return(0);
    499: }

    501: PetscErrorCode TSRKSetMultirate_RK(TS ts,PetscBool use_multirate)
    502: {
    503:   TS_RK          *rk = (TS_RK*)ts->data;

    508:   rk->use_multirate = use_multirate;
    509:   if (use_multirate) {
    510:     rk->dtratio = 2;
    511:     PetscObjectComposeFunction((PetscObject)ts,"TSSetUp_RK_MultirateSplit_C",TSSetUp_RK_MultirateSplit);
    512:     PetscObjectComposeFunction((PetscObject)ts,"TSReset_RK_MultirateSplit_C",TSReset_RK_MultirateSplit);
    513:     PetscObjectComposeFunction((PetscObject)ts,"TSSetUp_RK_MultirateNonsplit_C",TSSetUp_RK_MultirateNonsplit);
    514:     PetscObjectComposeFunction((PetscObject)ts,"TSReset_RK_MultirateNonsplit_C",TSReset_RK_MultirateNonsplit);
    515:   } else {
    516:     rk->dtratio = 0;
    517:     PetscObjectComposeFunction((PetscObject)ts,"TSSetUp_RK_MultirateSplit_C",NULL);
    518:     PetscObjectComposeFunction((PetscObject)ts,"TSReset_RK_MultirateSplit_C",NULL);
    519:     PetscObjectComposeFunction((PetscObject)ts,"TSSetUp_RK_MultirateNonsplit_C",NULL);
    520:     PetscObjectComposeFunction((PetscObject)ts,"TSReset_RK_MultirateNonsplit_C",NULL);
    521:   }
    522:   return(0);
    523: }

    525: PetscErrorCode TSRKGetMultirate_RK(TS ts,PetscBool *use_multirate)
    526: {
    527:   TS_RK *rk = (TS_RK*)ts->data;

    531:   *use_multirate = rk->use_multirate;
    532:   return(0);
    533: }