[Octave-bug-tracker] [bug #59488] eigs error in dsaupd for zero matrix

[Rik]

Update of bug #59488 (project octave):

                Severity:              3 - Normal => 2 - Minor              
                Priority:              5 - Normal => 3 - Low                
                 Release:                  6.0.92 => dev                    

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Follow-up Comment #14:

Before a programmer can make use of eigenvalues and eigenvectors, they have to
have some understanding of the linear algebra involved.  An all-zeros matrix
doesn't represent any useful linear transformation so it won't be encountered
in a practical case where a programmer is modeling a real-world phenomenon. 
Maybe somebody doing something in pure math would have a zero-transform that
changes all inputs in a vector space in to the zero vector, but the pure math
folks don't need a numerical computation language for that, they can work this
out symbolically with pen and paper.

The all-zeros matrix is a corner case for which it would be nice to return a
value, rather than an error, but isn't critical to most Octave users.

But, I have noticed some issues with the documentation, input validation, and
naming conventions within eigs.m.  I've got most of a changeset prepared which
fixes these items as well as handling the case of an all-zeros matrix.  I plan
to check the code in on the development branch later today.

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