[petsc-users] how to use schur fieldsplit preconditioner twice ~

[Liang ZHENG]

Hi, all,

I wrote a code as following:

void petsc_solve_thm2d(type_matrix_petsc *matrix)
{
  IS isg[4],iss,isf;
  MSGS("[petsc] Set blocked preconditioner index");

  PetscScalar np_Sv=matrix->np_col/3;
  PetscScalar np_Sp=matrix->np_col/6;
  PetscScalar np_Fv=matrix->np_col/3;
  PetscScalar np_Fp=matrix->np_col/6;

  ISCreateStride(PETSC_COMM_SELF,np_Sv,0,1,&isg[0]);
  ISCreateStride(PETSC_COMM_SELF,np_Sp,np_Sv,1,&isg[1]);
  ISCreateStride(PETSC_COMM_SELF,np_Fv,np_Sv+np_Sp,1,&isg[2]);
  ISCreateStride(PETSC_COMM_SELF,np_Fp,np_Sv+np_Sp+np_Fv,1,&isg[3]);

  IS is_solid[]={isg[0],isg[1]};
  IS is_fluid[]={isg[2],isg[3]};

  ierr = ISConcatenate(PETSC_COMM_SELF,2,is_solid,&iss);CHKERRV(ierr);
  ierr = ISConcatenate(PETSC_COMM_SELF,2,is_fluid,&isf);CHKERRV(ierr);

  MSGS("[petsc] Create solver");
  ierr = KSPCreate(PETSC_COMM_SELF,&matrix->ksp);CHKERRV(ierr);
  ierr = KSPSetOptionsPrefix(matrix->ksp,"thm_");CHKERRV(ierr);
  ierr = KSPSetOperators(matrix->ksp,matrix->LHS,matrix->LHS);CHKERRV(ierr);
  ierr = KSPSetFromOptions(matrix->ksp);CHKERRV(ierr);
  ierr = KSPGetPC(matrix->ksp,&matrix->pc);CHKERRV(ierr);

//  ierr = PCFieldSplitSetIS(matrix->pc,"Sv",isg[0]);CHKERRV(ierr);
//  ierr = PCFieldSplitSetIS(matrix->pc,"Sp",isg[1]);CHKERRV(ierr);
//  ierr = PCFieldSplitSetIS(matrix->pc,"Fv",isg[2]);CHKERRV(ierr);
//  ierr = PCFieldSplitSetIS(matrix->pc,"Fp",isg[3]);CHKERRV(ierr);

  ierr = PCFieldSplitSetIS(matrix->pc,"S",iss);CHKERRV(ierr);
  ierr = PCFieldSplitSetIS(matrix->pc,"F",isf);CHKERRV(ierr);

  //ierr = PCFieldSplitSetBlockSize(matrix->pc,4);CHKERRV(ierr);

  MSGS("[petsc] Solving");
  ierr = KSPSolve(matrix->ksp,matrix->RHS,matrix->SOL);CHKERRV(ierr);

  MSGS("[petsc] Destroy solver");
  ierr = KSPDestroy(&matrix->ksp);CHKERRV(ierr);
  ierr = ISDestroy(&isg);CHKERRV(ierr);
}

then I can call petsc in the command line as:

./thm2d_nonuniform  -thm_ksp_monitor -thm_ksp_view -thm_ksp_type fgmres
-thm_ksp_rtol 1e-10 -thm_pc_type fieldsplit  -thm_pc_fieldsplit_type schur
-thm_pc_fieldsplit_S_ksp_type fgmres -thm_fieldsplit_S_pc_type lu
-thm_pc_fieldsplit_F_ksp_type fgmres  -thm_fieldsplit_F_pc_type lu
-thm_fieldsplit_S_pc_factor_mat_solver_package umfpack

this command is working. but I also want to set  -thm_fieldsplit_S_pc_type
using fieldsplit schur preconditioner. Is there a solution to do something
like:

-thm_fieldsplit_S_pc_type fieldsplit -thm_fieldsplit_S_pc_field_type schur
-thm_fieldsplit_S_fieldsplit_Sv_ksp_type xxx
-thm_fieldsplit_S_fieldsplit_Sp_ksp_type xxx
-thm_fieldsplit_S_fieldsplit_Sv_pc_type xxx -
thm_fieldsplit_S_fieldsplit_Sp_pc_type xxx

Thanks a lot ~

Cheers,
Larry
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