If the problem is that the vector is not of nest type, you can overload the createVecs for the python matrix type, see e.g. https://urldefense.us/v3/__https://petsc.org/release/petsc4py/petsc_python_types.html__;!!G_uCfscf7eWS!aZjDCYTy1PCHmDJYxODxFR7QrOBVMVDa5NcHQ12xgd56_59kgzghGzTR42NjUnNXhIPGEMTWdWtzqqPdtK9UtT_taE4lvMw$
Stefano On Thu, Aug 7, 2025, 19:52 Moral Sanchez, Elena < elena.moral.sanc...@ipp.mpg.de> wrote: > Hello, > I want to solve a linear system with conjugate gradient and multigrid > preconditioner. I am using petsc4py. The solution is a Vector of type NEST > and the operator is a matrix-free operator created using > PETSc.Mat().createPython. The restriction and interpolation operators are > all type NEST and their VecType is set to NEST. As smoother I am using CG > without preconditioner. For the moment I am just using a classical V-cycle > with 2 levels. > > I am able to solve the system with CG without the MG preconditioner. > However, when I try to solve it with the MG preconditioner, it throws this > error: > > Traceback (most recent call last): > File "/home/elena-hp/code/Poisson_MG_Petsc.py", line 321, in <module> > solver.solve(b, u) > File "petsc4py/PETSc/KSP.pyx", line 1782, in petsc4py.PETSc.KSP.solve > petsc4py.PETSc.Error: error code 62 > [0] KSPSolve() at /home/elena-hp/petsc/src/ksp/ksp/interface/itfunc.c:1089 > [0] KSPSolve_Private() at /home/elena-hp/petsc/src/ksp/ksp/interface/ > itfunc.c:912 > [0] KSPSolve_CG() at /home/elena-hp/petsc/src/ksp/ksp/impls/cg/cg.c:213 > [0] KSP_PCApply() at /home/elena-hp/petsc/include/petsc/private/ > kspimpl.h:414 > [0] PCApply() at /home/elena-hp/petsc/src/ksp/pc/interface/precon.c:528 > [0] PCApply_MG() at /home/elena-hp/petsc/src/ksp/pc/impls/mg/mg.c:651 > [0] PCApply_MG_Internal() at /home/elena-hp/petsc/src/ksp/pc/impls/mg/ > mg.c:629 > [0] PCMGMCycle_Private() at /home/elena-hp/petsc/src/ksp/pc/impls/mg/ > mg.c:27 > [0] KSPSolve() at /home/elena-hp/petsc/src/ksp/ksp/interface/itfunc.c:1089 > [0] KSPSolve_Private() at /home/elena-hp/petsc/src/ksp/ksp/interface/ > itfunc.c:912 > [0] KSPSolve_CG() at /home/elena-hp/petsc/src/ksp/ksp/impls/cg/cg.c:162 > [0] VecCopy() at /home/elena-hp/petsc/src/vec/vec/interface/vector.c:1796 > [0] VecCopyAsync_Private() at /home/elena-hp/petsc/src/vec/vec/interface/ > vector.c:1755 > [0] VecCopy_Nest() at /home/elena-hp/petsc/src/vec/vec/impls/nest/ > vecnest.c:56 > [0] Invalid argument > [0] Nest vector argument 2 not setup. > > The error does not appear when the operator is also of type NEST and the > VecType is set to NEST. Unfortunately, for my application I cannot write > the operator as type NEST. > > I think that the problem is related to the fact that the method > createVecs() of the matrix-free operator does not return NEST vectors. I > tried to do setVecType(PETSc.Vec.Type.NEST) on the matrix-free operator but > when I call createVecs() it throws this error: > > Traceback (most recent call last): > File "petsc4py/PETSc/libpetsc4py.pyx", line 965, in > petsc4py.PETSc.MatCreateVecs_Python > petsc4py.PETSc.Error: error code 86 > [0] MatCreateVecs() at /home/elena-hp/petsc/src/mat/interface/ > matrix.c:9557 > [0] VecSetType() at /home/elena-hp/petsc/src/vec/vec/interface/ > vecreg.c:140 > [0] Unknown type. Check for miss-spelling or missing package: > https://urldefense.us/v3/__https://petsc.org/release/install/install/*external-packages__;Iw!!G_uCfscf7eWS!aZjDCYTy1PCHmDJYxODxFR7QrOBVMVDa5NcHQ12xgd56_59kgzghGzTR42NjUnNXhIPGEMTWdWtzqqPdtK9UtT_tTSSXMDQ$ > > <https://urldefense.us/v3/__https://petsc.org/release/install/install/*external-packages__;Iw!!G_uCfscf7eWS!dEBOuSXxIqEDpI33Xza0TlRPC5n6sN3fXNslohXzfITEmMwZLwQWJUTyNE-mMJHiXZjxQ-OlWu5625crKTR81qTlPMyhvkR09mUB$> > [0] Unknown vector type: nest > > The above exception was the direct cause of the following exception: > > Traceback (most recent call last): > File "<string>", line 1, in <module> > File "petsc4py/PETSc/Mat.pyx", line 3411, in > petsc4py.PETSc.Mat.createVecs > petsc4py.PETSc.Error: error code 101 > [0] MatCreateVecs() at /home/elena-hp/petsc/src/mat/interface/ > matrix.c:9552 > > Do you know how to fix this? > > Thank you in advance. > > Regards, > Elena >
