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[Octave-bug-tracker] [bug #57185] eigs does not consistently order eigen

From: Rik
Subject: [Octave-bug-tracker] [bug #57185] eigs does not consistently order eigenvalues
Date: Sat, 9 Nov 2019 14:39:44 -0500 (EST)
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko

Update of bug #57185 (project octave):

                Severity:           4 - Important => 3 - Normal             
              Item Group:       Inaccurate Result => Matlab Compatibility   
                 Summary: svds returns inconsistent singular values => eigs
does not consistently order eigenvalues


Follow-up Comment #12:

The issue of the ordering of singular values depends on the underlying
function eigs().  That function does not guarantee a particular ordering. 
However, Matlab has changed behavior relatively recently (R2017b).  They now

Behavior changed in R2017b

    Changes to sorting order of output

    eigs now sorts the output according to the value of sigma. For example,
the command eigs(A,k,'largestabs') produces k eigenvalues sorted in descending
order by magnitude.

    Previously, the sorting order of the output produced by eigs was not


    Calling eigs multiple times in succession now produces the same result.
Set 'StartVector' to a random vector to change this behavior.


    A display value of 2 no longer returns timing information. Instead, eigs
treats a value of 2 the same as a value of 1. Also, the messages shown by the
'Display' option have changed. The new messages show the residual in each
iteration, instead of the Ritz values.

Re-titling bug report to reflect underlying issue.


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