shift-invert transformation problem with slepc

[Anton Ermakov]

Dear All,

I am trying to use a shift-invert transformation in step-36. I did minimal changes in the solve function adding the following code that describes what spectral transformation I need to do:

SolverControl solver_control (dof_handler.n_dofs(), 1e-9);

SLEPcWrappers::SolverKrylovSchur eigensolver(solver_control);

eigensolver.set_which_eigenpairs (EPS_SMALLEST_REAL);

eigensolver.set_problem_type (EPS_GHEP);

double eigen_shift = 1.0e-4;

SLEPcWrappers::TransformationShiftInvert::AdditionalData additional_data(eigen_shift);

SLEPcWrappers::TransformationShiftInvert shift (MPI_COMM_WORLD, additional_data);

eigensolver.set_transformation (shift);

eigensolver.solve(stiffness_matrix,

                      mass_matrix,

                      eigenvalues,

                      eigenfunctions,

                      eigenfunctions.size());

and it gives me the following error: 

[0]PETSC ERROR: Shift-and-invert requires a target 'which' (see EPSSetWhichEigenpairs), for instance -st_type sinvert -eps_target 0 -eps_target_magnitude

Any help to resolve this error is greatly appreciated. I also attached the full code of modified step-36.

Thank you,

Anton.

[simon...@gmail.com]

Hi,

I think you need to set both which eigen pair and the target value. For example, if you look for the eigenvalue closest in magnitude to 0, you need to set the following

const double target_eigenvalue = 0;
eigensolver.set_which_eigenpairs(EPS_TARGET_MAGNITUDE);
eigensolver.set_target_eigenvalue(target_eigenvalue);

Depending on slepc version it might be that you can only choose EPS_TARGET_MAGNITUDE. See question 8 here:

https://slepc.upv.es/documentation/faq.htm

Best,
Simon

[Anton Ermakov]

Ok, I see - it is that EPS_TARGET_MAGNITUDE flag that was missing. It works now! Thanks a lot, Simon.

Anton.