1: #include <petsc/private/tsimpl.h>

  3: static PetscErrorCode TSAdaptChoose_CFL(TSAdapt adapt, TS ts, PetscReal h, PetscInt *next_sc, PetscReal *next_h, PetscBool *accept, PetscReal *wlte, PetscReal *wltea, PetscReal *wlter)
  4: {
  5:   PetscReal        hcfl, cfltimestep, ccfl;
  6:   PetscInt         ncandidates;
  7:   const PetscReal *ccflarray;

  9:   PetscFunctionBegin;
 10:   PetscCall(TSGetCFLTime(ts, &cfltimestep));
 11:   PetscCall(TSAdaptCandidatesGet(adapt, &ncandidates, NULL, NULL, &ccflarray, NULL));
 12:   ccfl = (ncandidates > 0) ? ccflarray[0] : 1.0;

 14:   PetscCheck(adapt->always_accept, PetscObjectComm((PetscObject)adapt), PETSC_ERR_SUP, "Step rejection not implemented. The CFL implementation is incomplete/unusable");

 16:   /* Determine whether the step is accepted of rejected */
 17:   *accept = PETSC_TRUE;
 18:   if (h > cfltimestep * ccfl) {
 19:     if (adapt->always_accept) {
 20:       PetscCall(PetscInfo(adapt, "Step length %g with scheme of CFL coefficient %g did not satisfy user-provided CFL constraint %g, proceeding anyway\n", (double)h, (double)ccfl, (double)cfltimestep));
 21:     } else {
 22:       PetscCall(PetscInfo(adapt, "Step length %g with scheme of CFL coefficient %g did not satisfy user-provided CFL constraint %g, step REJECTED\n", (double)h, (double)ccfl, (double)cfltimestep));
 23:       *accept = PETSC_FALSE;
 24:     }
 25:   }

 27:   /* The optimal new step based purely on CFL constraint for this step. */
 28:   hcfl = adapt->safety * cfltimestep * ccfl;
 29:   if (hcfl < adapt->dt_min) {
 30:     PetscCall(PetscInfo(adapt, "Cannot satisfy CFL constraint %g (with %g safety) at minimum time step %g with method coefficient %g, proceeding anyway\n", (double)cfltimestep, (double)adapt->safety, (double)adapt->dt_min, (double)ccfl));
 31:   }

 33:   *next_sc = 0;
 34:   *next_h  = PetscClipInterval(hcfl, adapt->dt_min, adapt->dt_max);
 35:   *wlte    = -1; /* Weighted local truncation error was not evaluated */
 36:   *wltea   = -1; /* Weighted absolute local truncation error was not evaluated */
 37:   *wlter   = -1; /* Weighted relative local truncation error was not evaluated */
 38:   PetscFunctionReturn(PETSC_SUCCESS);
 39: }

 41: /*MC
 42:    TSADAPTCFL - CFL adaptive controller for time stepping

 44:    Level: intermediate

 46: .seealso: [](ch_ts), `TS`, `TSAdapt`, `TSGetAdapt()`, `TSAdaptType`
 47: M*/
 48: PETSC_EXTERN PetscErrorCode TSAdaptCreate_CFL(TSAdapt adapt)
 49: {
 50:   PetscFunctionBegin;
 51:   adapt->ops->choose = TSAdaptChoose_CFL;
 52:   PetscFunctionReturn(PETSC_SUCCESS);
 53: }