Date: 2021-03-03T22:27:52+00:00

Actual source code: euler.c
petsc-3.14.5 2021-03-03
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      1: /*
      2:        Code for Timestepping with explicit Euler.
      3: */
      4: #include <petsc/private/tsimpl.h>

      6: typedef struct {
      7:   Vec update;     /* work vector where new solution is formed  */
      8: } TS_Euler;

     10: static PetscErrorCode TSStep_Euler(TS ts)
     11: {
     12:   TS_Euler       *euler = (TS_Euler*)ts->data;
     13:   Vec            solution = ts->vec_sol,update = euler->update;
     14:   PetscBool      stageok,accept = PETSC_TRUE;
     15:   PetscReal      next_time_step = ts->time_step;

     19:   TSPreStage(ts,ts->ptime);
     20:   TSComputeRHSFunction(ts,ts->ptime,solution,update);
     21:   VecAYPX(update,ts->time_step,solution);
     22:   TSPostStage(ts,ts->ptime,0,&solution);
     23:   TSAdaptCheckStage(ts->adapt,ts,ts->ptime,solution,&stageok);
     24:   if (!stageok) {ts->reason = TS_DIVERGED_STEP_REJECTED; return(0);}
     25:   TSFunctionDomainError(ts,ts->ptime+ts->time_step,update,&stageok);
     26:   if (!stageok) {ts->reason = TS_DIVERGED_STEP_REJECTED; return(0);}

     28:   TSAdaptChoose(ts->adapt,ts,ts->time_step,NULL,&next_time_step,&accept);
     29:   if (!accept) {ts->reason = TS_DIVERGED_STEP_REJECTED; return(0);}
     30:   VecCopy(update,solution);

     32:   ts->ptime += ts->time_step;
     33:   ts->time_step = next_time_step;
     34:   return(0);
     35: }
     36: /*------------------------------------------------------------*/

     38: static PetscErrorCode TSSetUp_Euler(TS ts)
     39: {
     40:   TS_Euler       *euler = (TS_Euler*)ts->data;

     44:   TSCheckImplicitTerm(ts);
     45:   VecDuplicate(ts->vec_sol,&euler->update);
     46:   TSGetAdapt(ts,&ts->adapt);
     47:   TSAdaptCandidatesClear(ts->adapt);
     48:   return(0);
     49: }

     51: static PetscErrorCode TSReset_Euler(TS ts)
     52: {
     53:   TS_Euler       *euler = (TS_Euler*)ts->data;

     57:   VecDestroy(&euler->update);
     58:   return(0);
     59: }

     61: static PetscErrorCode TSDestroy_Euler(TS ts)
     62: {

     66:   TSReset_Euler(ts);
     67:   PetscFree(ts->data);
     68:   return(0);
     69: }
     70: /*------------------------------------------------------------*/

     72: static PetscErrorCode TSSetFromOptions_Euler(PetscOptionItems *PetscOptionsObject,TS ts)
     73: {
     75:   return(0);
     76: }

     78: static PetscErrorCode TSView_Euler(TS ts,PetscViewer viewer)
     79: {
     81:   return(0);
     82: }

     84: static PetscErrorCode TSInterpolate_Euler(TS ts,PetscReal t,Vec X)
     85: {
     86:   TS_Euler       *euler = (TS_Euler*)ts->data;
     87:   Vec            update = euler->update;
     88:   PetscReal      alpha = (ts->ptime - t)/ts->time_step;

     92:   VecWAXPY(X,-ts->time_step,update,ts->vec_sol);
     93:   VecAXPBY(X,1.0-alpha,alpha,ts->vec_sol);
     94:   return(0);
     95: }

     97: static PetscErrorCode TSComputeLinearStability_Euler(TS ts,PetscReal xr,PetscReal xi,PetscReal *yr,PetscReal *yi)
     98: {
    100:   *yr = 1.0 + xr;
    101:   *yi = xi;
    102:   return(0);
    103: }
    104: /* ------------------------------------------------------------ */

    106: /*MC
    107:       TSEULER - ODE solver using the explicit forward Euler method

    109:   Level: beginner

    111: .seealso:  TSCreate(), TS, TSSetType(), TSBEULER

    113: M*/
    114: PETSC_EXTERN PetscErrorCode TSCreate_Euler(TS ts)
    115: {
    116:   TS_Euler       *euler;

    120:   PetscNewLog(ts,&euler);
    121:   ts->data = (void*)euler;

    123:   ts->ops->setup           = TSSetUp_Euler;
    124:   ts->ops->step            = TSStep_Euler;
    125:   ts->ops->reset           = TSReset_Euler;
    126:   ts->ops->destroy         = TSDestroy_Euler;
    127:   ts->ops->setfromoptions  = TSSetFromOptions_Euler;
    128:   ts->ops->view            = TSView_Euler;
    129:   ts->ops->interpolate     = TSInterpolate_Euler;
    130:   ts->ops->linearstability = TSComputeLinearStability_Euler;
    131:   ts->default_adapt_type   = TSADAPTNONE;
    132:   ts->usessnes             = PETSC_FALSE;
    133:   return(0);
    134: }