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[Octave-bug-tracker] [bug #46683] Need better configure test for bad ARP

From: Marco Caliari
Subject: [Octave-bug-tracker] [bug #46683] Need better configure test for bad ARPACK library
Date: Tue, 12 Jan 2016 09:26:03 +0000
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:43.0) Gecko/20100101 Firefox/43.0

Follow-up Comment #20, bug #46683 (project octave):

Here my first example that I cannot reproduce in plain fortran. The matrix is
AA (taken from #31479), the initial vector opts.v0

A = [1,0,0,-1;0,1,0,0;0,0,1,0;0,0,2,1];
AA = sparse([A,zeros(4),zeros(4);zeros(4),A,zeros(4);zeros(4),zeros(4),A]);
opts.v0 =

and I use eigs(AA,1,'lm',opts). I get  1.0000e+00 - 2.8107e-06i (Octave 4.0.0,
arpack 3.3.0). From line 296 in __eigs__.cc I understand have_sigma = false
and then EigsRealNonSymmetricMatrix should be used (see line 584). In
eigs_base.cc, line 1696, mode=1 (regular mode) and in line 1731, p=n-1=11. So,
it should correspond to dndrv1.f (attached). But here the result has imaginary
part exactly zero (as in Matlab, by the way).

(file #35998)

Additional Item Attachment:

File name: dndrv1.f                       Size:14 KB


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