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error message about "eigs" function

Asked by Chong Hou on 3 Feb 2012
Latest activity Edited by Matt J
on 27 Sep 2013
I use function eigs(A,1,'sm') in my code, and when I run it, sometimes there is the error message saying "Error using eigs (line 254) Error with ARPACK routine dnaupd: info = -9". What does that mean? Thanks!
The matrix A is a real symmetric matrix in my code, though sometimes it might be singular.

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Answer by Walter Roberson
on 3 Feb 2012

c INFO Integer. (INPUT/OUTPUT)
c Error flag on output.
c = -9: Starting vector is zero.
This could occur if you supplied an options structure to eigs() and the v0 (starting column vector) field was all zero.

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Thank you Walter! Could you be more specific? Does the "v0 field" mean the first column of my matrix A?
No, the v0 field is a structure field named v0.
If you look at the possible syntaxes for eigs(), it lists,
eigs(A,K,sigma,opts)
eigs(A,B,k,sigma,opts)
In those situations, opts is a structure, and the v0 field would be a field in that structure.

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