Dear all, I am trying to experiment with a block Lanczos eigensolver code of mine for symmetric systems.
I have a practical question which I could not find a direct answer yet. For large sparse matrices, what should be the number of eigenvalues to be extracted with this Krylov subspace based solver? I am looking for a ratio or a rule of thumb like 'if you want k eigenvalues and your system size is n, then the ratio given by k/n should not exceed 0.01'. In this case '0.01' is just a coefficient, say r, any practical experience on choosing this coefficient r? I know Lanczos method is efficient on extracting extreme values over the spectrum but is there a, more or less, a practical limit like the one I tried to explain? Best regards, Umut
