Hello All,
I hope someone can help :) I think I am doing something wrong, but
cannot understand what. I have a huge time dependent system with 3d DMDA
data structure and I am evolving it with explicit Runge-Kutta by using
TS and basically only using "TSSetRHSFunction". Now I want to repeat it
with implicit time stepper (for now Crank-Nicolson) and I am trying to
provide finite difference Jacobian and I am failing miserably. I also
cannot find appropriate example in PETSc tutorial (if you can point me
to working example, it would be great).
Here is my best attempt (what wrong with it?):
DMDACreate3d(PETSC_COMM_WORLD, DM_BOUNDARY_PERIODIC,
DM_BOUNDARY_PERIODIC, DM_BOUNDARY_PERIODIC,
DMDA_STENCIL_STAR,
NX, NY, NZ,
PETSC_DECIDE, PETSC_DECIDE, PETSC_DECIDE,
2*3+NC*NS,
1,
NULL, NULL, NULL, &da);
DMSetUp(da);
DMCreateGlobalVector(da,&x);
TSCreate(PETSC_COMM_WORLD,&ts);
TSSetProblemType(ts,TS_NONLINEAR);
TSSetRHSFunction(ts,NULL,compute_RHS,NULL);
TSSetMaxTime(ts,T_FINAL);
TSSetExactFinalTime(ts,TS_EXACTFINALTIME_STEPOVER);
TSSetDM(ts,da);
TSSetType(ts,TSCN); //it works with: TSSetType(ts,TSRK);
set_IC(da,x);
TSSetTimeStep(ts,DT);
TSSetSolution(ts,x);
TSGetSNES(ts,&snes);
SNESGetKSP(snes,&ksp);
KSPGetPC(ksp,&pc);
PCSetType(pc,PCNONE);
DMSetMatType(da,MATAIJ);
DMCreateMatrix(da,&J);
ISColoring iscoloring;
MatFDColoring matfdcoloring;
DMCreateColoring(da,IS_COLORING_GLOBAL,&iscoloring);
MatFDColoringCreate(J,iscoloring,&matfdcoloring);
MatFDColoringSetType(matfdcoloring,MATMFFD_DS);
// I think I do something wrong in the following 3 lines
PetscErrorCode (*temp_f)(SNES,Vec,Vec,void*);
SNESGetFunction(snes,NULL,&temp_f,NULL);
MatFDColoringSetFunction(matfdcoloring,(PetscErrorCode
(*)(void))temp_f,NULL);
MatFDColoringSetUp(J,iscoloring,matfdcoloring);
SNESSetJacobian(snes,J,J,SNESComputeJacobianDefaultColor,matfdcoloring);
ISColoringDestroy(&iscoloring);
TSSolve(ts,x);
Thank you,
Oleksandr Koshkarov.
