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

[Michael Werner]

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.