[petsc-users] slepc4py - Using shell matrix and explicit preconditioning matrix to solve EPS

[Jose E. Roman]

Try calling E.setUp() before replacing the matrix. But note that E.setUp() will try to build the preconditioner, so you will have to set PC=none and later change it to lu.

Also note that in Krylov methods with exact shift-and-invert (LU) the preconditioner matrix should be exactly the same as A-sigma*B, otherwise you may get unexpected results. Davidson-type methods allow using a different preconditioner.

Jose

> El 1 ago 2018, a las 10:11, Michael Werner <michael.werner at dlr.de> escribió:
> 
> Hello,
> 
> I'm trying to find the smallest eigenvalues of a linear system created by CFD simulations. To reduce memory requirements, I want to use a shell matrix (A_Shell) to provide the matrix-vector product, and a lower-order explicit matrix (P) as preconditioner. As I'm solving a generalized problem, I'm also passing a second explicit matrix (B) to the EPS. However, I don't see a way to provide the explicit preconditioning matrix to the EPS.
> 
> I'm using the following options: -st_type sinvert -st_pc_type lu -st_matmode shell -eps_target 0.01 -eps_target_real  My Python code looks like this:
> 
> E = SLEPc.EPS().create(comm=PETSc.COMM_WORLD)
> E.setOperators(A_Shell, B)
> E.setProblemType(SLEPc.EPS.ProblemType.GNHEP)
> st = E.getST()
> ksp = st.getKSP()
> pc = ksp.getPC()
> pc.setOperators(A_Shell, P)
> E.setFromOptions()
> E.solve()
> 
> If I run this, I get the following error:
>> Error: error code 92
>> [2] EPSSolve() line 135 in /home/conda/feedstock_root/build_artifacts/slepc_1531127798016/work/src/eps/interface/epssolve.c
>> [2] EPSSetUp() line 263 in /home/conda/feedstock_root/build_artifacts/slepc_1531127798016/work/src/eps/interface/epssetup.c
>> [2] STSetUp() line 271 in /home/conda/feedstock_root/build_artifacts/slepc_1531127798016/work/src/sys/classes/st/interface/stsolve.c
>> [2] STSetUp_Sinvert() line 132 in /home/conda/feedstock_root/build_artifacts/slepc_1531127798016/work/src/sys/classes/st/impls/sinvert/sinvert.c
>> [2] KSPSetUp() line 381 in /home/conda/feedstock_root/build_artifacts/petsc_1530637062977/work/src/ksp/ksp/interface/itfunc.c
>> [2] PCSetUp() line 923 in /home/conda/feedstock_root/build_artifacts/petsc_1530637062977/work/src/ksp/pc/interface/precon.c
>> [2] PCSetUp_LU() line 113 in /home/conda/feedstock_root/build_artifacts/petsc_1530637062977/work/src/ksp/pc/impls/factor/lu/lu.c
>> [2] MatGetFactor() line 4332 in /home/conda/feedstock_root/build_artifacts/petsc_1530637062977/work/src/mat/interface/matrix.c
>> [2] See http://www.mcs.anl.gov/petsc/documentation/linearsolvertable.html for possible LU and Cholesky solvers
>> [2] MatSolverType mumps does not support matrix type shell
> 
> I also tried setting up the preconditioner in advance, but that didn't work either and produced the same errors as above:
> 
> pc = PETSc.PC().create(comm=PETSc.COMM_WORLD)
> pc.setOperators(A_Shell, P)
> pc.setFromOptions()
> pc.setUp()
> 
> E = SLEPc.EPS().create(comm=PETSc.COMM_WORLD)
> E.setOperators(A_Shell, B)
> E.setProblemType(SLEPc.EPS.ProblemType.GNHEP)
> ksp = E.getKSP()
> ksp.setPC(pc)
> E.setFromOptions()
> E.solve()
> 
> If I simply try to solve a KSP with those two matrices, it works without any problems.