[Octave-bug-tracker] [bug #49523] eigs (R2013b and later) uses NaNs, not zeros, for unconverged Ritz values

[Rik]

Follow-up Comment #7, bug #49523 (project octave):

I don't see any real difference in creating matrices with all zeros or all
NaNs.  See below


octave:1> tic; x = zeros (1e3,1e3); toc
Elapsed time is 0.00626612 seconds.
octave:2> tic; x = zeros (1e3,1e3); toc
Elapsed time is 0.00639701 seconds.
octave:3> tic; x = NaN (1e3,1e3); toc
Elapsed time is 0.00226998 seconds.
octave:4> tic; x = NaN (1e3,1e3); toc
Elapsed time is 0.00632405 seconds.
octave:5> tic; x = NaN (1e3,1e3); toc
Elapsed time is 0.00363517 seconds.


I don't think performance is an issue here.  And I have always tried to code
Octave to avoid Garbage In / Garbage Out phenomena.  I believe many Octave
users are professional scientists first, and coders second.  I don't think
they will necessarily realize that they need to code defensively and check
their eigenvalues before going on to use the eigenvectors.  For that reason, I
would prefer to return NaNs for the eigenvectors to immediately inform the
coder that something is amiss.


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