1: static char help[] = "Solves DAE with integrator only on non-algebraic terms \n";

  3:  #include <petscts.h>

  5: /*
  6:         \dot{U} = f(U,V)
  7:         F(U,V)  = 0
  8: */


 11: /*
 12:    f(U,V) = U + V

 14: */
 15: PetscErrorCode f(PetscReal t,Vec U,Vec V,Vec F)
 16: {

 20:   VecWAXPY(F,1.0,U,V);
 21:   return(0);
 22: }

 24: /*
 25:    F(U,V) = U - V

 27: */
 28: PetscErrorCode F(PetscReal t,Vec U,Vec V,Vec F)
 29: {

 33:   VecWAXPY(F,-1.0,V,U);
 34:   return(0);
 35: }

 37: typedef struct {
 38:   PetscReal      t;
 39:   SNES           snes;
 40:   Vec            U,V;
 41:   PetscErrorCode (*f)(PetscReal,Vec,Vec,Vec);
 42:   PetscErrorCode (*F)(PetscReal,Vec,Vec,Vec);
 43: } AppCtx;

 45: extern PetscErrorCode TSFunction(TS,PetscReal,Vec,Vec,void*);
 46: extern PetscErrorCode SNESFunction(SNES,Vec,Vec,void*);

 48: int main(int argc,char **argv)
 49: {
 51:   AppCtx         ctx;
 52:   TS             ts;
 53:   Vec            tsrhs,U;

 55:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
 56:   TSCreate(PETSC_COMM_WORLD,&ts);
 57:   TSSetProblemType(ts,TS_NONLINEAR);
 58:   TSSetType(ts,TSEULER);
 59:   TSSetFromOptions(ts);
 60:   VecCreateMPI(PETSC_COMM_WORLD,PETSC_DECIDE,1,&tsrhs);
 61:   VecCreateMPI(PETSC_COMM_WORLD,PETSC_DECIDE,1,&U);
 62:   TSSetRHSFunction(ts,tsrhs,TSFunction,&ctx);
 63:   ctx.f = f;

 65:   SNESCreate(PETSC_COMM_WORLD,&ctx.snes);
 66:   SNESSetFromOptions(ctx.snes);
 67:   SNESSetFunction(ctx.snes,NULL,SNESFunction,&ctx);
 68:   SNESSetJacobian(ctx.snes,NULL,NULL,SNESComputeJacobianDefault,&ctx);
 69:   ctx.F = F;
 70:   VecCreateMPI(PETSC_COMM_WORLD,PETSC_DECIDE,1,&ctx.V);

 72:   VecSet(U,1.0);
 73:   TSSolve(ts,U);

 75:   VecDestroy(&ctx.V);
 76:   VecDestroy(&tsrhs);
 77:   VecDestroy(&U);
 78:   SNESDestroy(&ctx.snes);
 79:   TSDestroy(&ts);
 80:   PetscFinalize();
 81:   return ierr;
 82: }

 84: /*
 85:    Defines the RHS function that is passed to the time-integrator. 

 87:    Solves F(U,V) for V and then computes f(U,V)

 89: */
 90: PetscErrorCode TSFunction(TS ts,PetscReal t,Vec U,Vec F,void *actx)
 91: {
 92:   AppCtx         *ctx = (AppCtx*)actx;

 96:   ctx->t = t;
 97:   ctx->U = U;
 98:   SNESSolve(ctx->snes,NULL,ctx->V);
 99:   (*ctx->f)(t,U,ctx->V,F);
100:   return(0);
101: }

103: /*
104:    Defines the nonlinear function that is passed to the nonlinear solver

106: */
107: PetscErrorCode SNESFunction(SNES snes,Vec V,Vec F,void *actx)
108: {
109:   AppCtx         *ctx = (AppCtx*)actx;

113:   (*ctx->F)(ctx->t,ctx->U,V,F);
114:   return(0);
115: }