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[Octave-bug-tracker] [bug #52425] eigs function regresses


From: Marco Caliari
Subject: [Octave-bug-tracker] [bug #52425] eigs function regresses
Date: Mon, 20 Nov 2017 02:25:42 -0500 (EST)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0

Follow-up Comment #7, bug #52425 (project octave):

@A.R. Burgers: first, I strongly suggest you to upgrade to arpack 3.3.0, at
least. Before 3.2.0 arpack can compute wrong eigenvectors. Second, can you
find an explicit initial vector for eigs for which the first two values of


n = 20;
A = sparse ([3:n,1:n,1:(n-2)],[1:(n-2),1:n,3:n],...
[ones(1,n-2),4*ones(1,n),ones(1,n-2)]);
k = 4;
opts.v0 = something 20x1
d1 = eigs (A, k, "be", opts)


are 5.6825? This would make the example exactly reproducible.

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