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: }