I mean run with -eps_monitor (see section 2.5.3) and you will see if residuals are decreasing. Either increase the maximum number of iterations or the size of the subspace.
> El 13 feb 2020, a las 22:03, baikadi pranay <[email protected]> > escribió: > > Thank you Jose for the reply. > > If I set PETSC_DEFAULT_INTEGER for ncv as suggested in the EPSSetDimensions > documentation, I am still running into the same problem. Also, could you > elaborate on what you mean by checking convergence with a monitor. Do you > mean comparing the eigenvalues for ith and (i+1)th iterations and plotting > the difference to see convergence? > > Sincerely, > Pranay. > ᐧ > > On Thu, Feb 13, 2020 at 1:54 PM Jose E. Roman <[email protected]> wrote: > For nev=10 you are using a subspace of size 20. This may be too small. Check > convergence with a monitor and increase ncv if necessary. > > Jose > >> El 13 feb 2020, a las 21:25, baikadi pranay <[email protected]> >> escribió: >> >> >> Hello PETSc Users, >> >> I am trying to find the lowest 'n' eigenvalues of a hermitian eigenvalue >> problem. The size of the operator matrix (hamiltonian in my case) is >> dependent on the mesh spacing provided by the user (which is expected). >> However I have the following issue: >> >> The number of eigenvalues given by the solver is not consistent with what is >> given as input in the EPSSetDimensions routine. For example, for a >> 12000x12000 matrix, the solver gives 20 correct eigenvalues if nev=20, but >> fails to give any eigenvalue if nev=10. >> >> I am using the following lines of code to solve the problem: >> >> call EPSCreate(PETSC_COMM_WORLD,eps,ierr) >> call EPSSetOperators(eps,ham,PETSC_NULL_MAT,ierr) >> call EPSSetProblemType(eps,EPS_HEP,ierr) >> call EPSSetWhichEigenpairs(eps,EPS_SMALLEST_MAGNITUDE,ierr) >> call EPSSetDimensions(eps,n_sub,n_sub*2,PETSC_DEFAULT_INTEGER,ierr) >> call EPSSetTolerances(eps,1D-10,5000,ierr) >> call EPSSolve(eps,ierr) >> >> After the EPSSolve, I am calling EPSGetEigenPair and other relevant routines >> to get the eigenvector and eigenvalues. >> >> Any lead as to how to solve this problem would be greatly helpful to us. >> Please let me know if I need to provide any further information. >> >> Thank you for your time. >> >> Sincerely, >> Pranay. >>
