title: Why can't scipy compute all eigenvalues?
body: <p>The documentation of <a href="https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.linalg.eigs.html" rel="nofollow noreferrer">scipy.sparse.linalg.eigs</a> reads</p>
  <blockquote>
  <p>The number of eigenvalues and eigenvectors desired. k must be smaller than N-1. It is not possible to compute all eigenvectors of a matrix.</p>
  </blockquote>
  <p>Why can it not compute all eigenvalues? This is possible for standard (non-sparse) matrices.</p>