[Octave-bug-tracker] [bug #60924] DNAUPD did not find any eigenvalues to sufficient accuracy

[Rik]

Follow-up Comment #8, bug #60924 (project octave):

Since eigs() uses ARPACK underneath which is an iterative algorithm, the
choice of initial starting point will make a difference.  

You might try setting the initial location using field 'v0' of the option
structure and see if there is a value that always works.  Increasing the
number of basis vectors, field 'p', might also help.

Other options to try are 'maxit' for maximum iterations or reduce the
tolerance with 'tol'.

It may be that the error message is simply wrong.  It states that "dneupd:
DNAUPD did not find any eigenvalues to sufficient accuracy".  That part might
be true, and would simply mean that the user needs to adjust options to
achieve convergence.

The second part, "This should not happen.  Please, see
https://www.gnu.org/software/octave/bugs.html, and file a bug report" might be
incorrect.  Maybe for certain problems and combinations of input options
eigs() can fail to converge.

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