Richard Mills <[email protected]> writes: > Qin, > > Krylov methods will find the extreme eigenvalues first (unless you do > something in particular to get at the interior values), so this is what you > are getting from PETSc. > > Another thing to keep in mind is that the eigenvalue estimates using the > Hessenberg matrix from GMRES can be pretty terrible. If you want something > better, you may want to use something like Arnoldi/Lanczos or > Jacobi-Davidson. Yousef Saad's book at > http://www-users.cs.umn.edu/~saad/eig_book_2ndEd.pdf offers some great > explanations of these methods, which you can use via the PETSc-based SLEPc > package.
Agreed. Use SLEPc if you want actual eigenvalues or eigenvectors. You can target wherever you want.
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