[petsc-users] Use block Jacobi preconditioner with SNES

[Jed Brown]

"Smith, Barry F." <bsmith at mcs.anl.gov> writes:

>     I have added new functionality within SNES to allow one to do as you desire in the branch barry/feature-snessetkspsetupcallback. Please see src/snes/examples/tests/ex3.c 

Note that this example is block Jacobi with O(1) sparse blocks per
process, not variable-sized point-block Jacobi which I think is what Ali
had in mind.

>     Please let us know if it works for you and if you have any questions or problems.
>
>     Barry
>
>    Note that it has to be handled by a callback called from within the SNES solver because that is the first time the matrix exists in a form that the block sizes may be set.
>
>     Sorry for the runaround with so many emails. 
>
>
>> On Aug 24, 2018, at 3:48 PM, Ali Reza Khaz'ali <arkhazali at cc.iut.ac.ir> wrote:
>> 
>> Hi,
>> 
>> I am trying to use block Jacobi preconditioner in SNES (SNESNEWTONLS). However, PCBJacobiGetSubKSP function returns an error stating "Object is in wrong state, Must call KSPSetUp() or PCSetUp() first". When I add KSPSetUp, I got and error from them as: "Must call DMShellSetGlobalVector() or DMShellSetCreateGlobalVector()", and if PCSetUp is added, "Object is in wrong state, Matrix must be set first" error is printed.
>> 
>> Below is a part of my code. It is run serially. Any help is much appreciated.
>> 
>>     ierr = SNESGetKSP(snes, &Petsc_ksp);
>>     CHKERRQ(ierr);
>>     ierr = KSPGetPC(Petsc_ksp, &Petsc_pc);
>>     CHKERRQ(ierr);
>>     ierr = KSPSetTolerances(Petsc_ksp, 1.e-3, 1e-3, PETSC_DEFAULT, 20000);
>>     CHKERRQ(ierr);
>>     ierr = SNESSetTolerances(snes, 1e-1, 1e-1, 1e-1, 2000, 2000);
>>     CHKERRQ(ierr);
>>     ierr = SNESSetType(snes, SNESNEWTONLS);
>>     CHKERRQ(ierr);
>>     ierr = KSPSetType(Petsc_ksp, KSPGMRES);
>>     CHKERRQ(ierr);
>>     ierr = PCSetType(Petsc_pc, PCBJACOBI);
>>     CHKERRQ(ierr);
>>     ierr = PCSetType(Petsc_pc, PCBJACOBI);
>>     CHKERRQ(ierr);
>>     ierr = PCBJacobiSetTotalBlocks(Petsc_pc, 2*Nx*Ny*Nz, SadeqSize);
>>     CHKERRQ(ierr);
>> 
>>     SNESSetUp(snes);
>>     CHKERRQ(ierr);
>>     ierr = PCBJacobiGetSubKSP(Petsc_pc, &nLocal, &Firstly, &subKSP);
>>     CHKERRQ(ierr);
>> 
>>     for (i = 0; i < nLocal; i++) {
>>         ierr = KSPGetPC(subKSP[i], &SubPc);
>>         CHKERRQ(ierr);
>>         ierr = PCSetType(SubPc, PCLU);
>>         CHKERRQ(ierr);
>>         ierr = PCFactorSetMatSolverPackage(SubPc, "mkl_pardiso");
>>         CHKERRQ(ierr);
>>         ierr = KSPSetType(subKSP[i], KSPPREONLY);
>>         CHKERRQ(ierr);
>>         ierr = KSPSetTolerances(subKSP[i], 1.e-6, PETSC_DEFAULT, PETSC_DEFAULT, PETSC_DEFAULT);
>>         CHKERRQ(ierr);
>>     }
>>     ierr = SNESSolve(snes, NULL, Petsc_X);
>>     CHKERRQ(ierr);
>> 
>> 
>> 
>> -- 
>> Ali Reza Khaz’ali
>> Assistant Professor of Petroleum Engineering,
>> Department of Chemical Engineering
>> Isfahan University of Technology
>> Isfahan, Iran
>>