I'm having trouble using scipy.sparse.linalg.eigs in that it fails to find any eigenvalues hence raising a "DNAUPD did not find any eigenvalues to sufficient accuracy." error. Even after experimenting with different tol parameter settings. If instead I use scipy.linalg.eig after first calling .todense() on my sparse matrix I do get all the eigenvalues I expect to get back. I suppose I could just do this, but that seems a bit inelegant after all the trouble of working with sparse matrices. I realize this issue is a bit hard to answer if I don't provide a concrete example so quickly, but I just was wondering if anybody has experienced a similar problem perhaps? The eigenvalues which I expect to get back are N/2 complex conjugate pairs, where NxN is the size of my original matrix. Any help or advice is greatly appreciated.