Leonhard:
have you checked that the matrix really is invertible? We use the wrappers as
is for step-36, if I recall correctly. A good starting point for asking why
your approach doesn't work would be to ask what is different between your
program and step-36.
Best
W.
On 2/25/22 07:10, Léonhard YU wrote:
*** Caution: EXTERNAL Sender ***
Hello Everyone:
I am dealing with a eigenvalue problem with SLEPc, but the program reports
this error:
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Zero pivot in LU factorization:
https://petsc.org/release/faq/#zeropivot
[0]PETSC ERROR: Zero pivot row 1 value 0. tolerance 2.22045e-14
I have reviewed the documentation. It says that (Frequently Asked Questions
(FAQ) — PETSc 3.16.4 documentation
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpetsc.org%2Frelease%2Ffaq%2F%23zeropivot&data=04%7C01%7CWolfgang.Bangerth%40colostate.edu%7Cff03e4917646439d68e908d9f868a339%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637813950590384693%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=UcAsQKuwWtUlwHjMjn8IGvLRvUbs8O592okHh6M5fuY%3D&reserved=0>)
*A zero pivot in LU, ILU, Cholesky, or ICC sparse factorization does not
always mean that the matrix is singular. You can use*
*-pc_factor_shift_type nonzero -pc_factor_shift_amount [amount] *
*or*
*-pc_factor_shift_type positive_definite -[level]_pc_factor_shift_type nonzero
-pc_factor_shift_amount [amount] *
*or*
*-[level]_pc_factor_shift_type positive_definite *
*to prevent the zero pivot. [level] is “sub” when lu, ilu, cholesky, or icc
are employed in each individual block of the bjacobi or ASM preconditioner.
[level] is “mg_levels” or “mg_coarse” when lu, ilu, cholesky, or icc are used
inside multigrid smoothers or to the coarse grid solver. See
PCFactorSetShiftType
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpetsc.org%2Frelease%2Fdocs%2Fmanualpages%2FPC%2FPCFactorSetShiftType.html%23PCFactorSetShiftType&data=04%7C01%7CWolfgang.Bangerth%40colostate.edu%7Cff03e4917646439d68e908d9f868a339%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637813950590384693%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=zp3oMzA5JMPuOyVmMPXG3dGx4u1m0nGLcNVh4EmOmLs%3D&reserved=0>(),
PCFactorSetShiftAmount
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpetsc.org%2Frelease%2Fdocs%2Fmanualpages%2FPC%2FPCFactorSetShiftAmount.html%23PCFactorSetShiftAmount&data=04%7C01%7CWolfgang.Bangerth%40colostate.edu%7Cff03e4917646439d68e908d9f868a339%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637813950590384693%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=F85oRwsykILhaQjMn6lUfkDGQCXuHgl1ExpVllAVLAs%3D&reserved=0>().*
*This error can also happen if your matrix is singular, see MatSetNullSpace
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpetsc.org%2Frelease%2Fdocs%2Fmanualpages%2FMat%2FMatSetNullSpace.html%23MatSetNullSpace&data=04%7C01%7CWolfgang.Bangerth%40colostate.edu%7Cff03e4917646439d68e908d9f868a339%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637813950590384693%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=L3uPVPCwyJQF%2FqarLxETmnSrjdq5mCC2MXDXfR7bLCA%3D&reserved=0>() for
how to handle this. If this error occurs in the zeroth row of the matrix, it
is likely you have an error in the code that generates the matrix.*
So I write the code as follows:
*PETScWrappers::PreconditionBlockJacobi::AdditionalData data;
PETScWrappers::PreconditionBlockJacobi preconditioner(mpi_communicator,
data);
SolverControl linear_solver_control (dof_handler.n_dofs(),
1e-9, false, false);
PETScWrappers::SolverCG linear_solver(linear_solver_control,
mpi_communicator);
PCFactorSetShiftType(preconditioner.get_pc(), MAT_SHIFT_NONZERO);
// PCFactorSetShiftAmount(preconditioner.get_pc(), 3e-14);
linear_solver.initialize(preconditioner);
SolverControl solver_control (100, 1e-9,false,false);
SLEPcWrappers::SolverKrylovSchur eigensolver(solver_control,
mpi_communicator);
eigensolver.set_which_eigenpairs(EPS_SMALLEST_REAL);
eigensolver.set_problem_type(EPS_GHEP);
SLEPcWrappers::TransformationShift
spectral_transformation(mpi_communicator);
spectral_transformation.set_solver(linear_solver);
eigensolver.set_transformation(spectral_transformation);
eigensolver.solve(stiffness_matrix,
mass_matrix,
eigenvalues,
eigenfunctions,
eigenfunctions.size());*
But the error occurs as the same. I don't know how to solve it.
Thanks for your help.
Best Wishes.
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