error message about "eigs" function

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.

Answer 1

[Walter Roberson]

http://www.caam.rice.edu/software/ARPACK/UG/node137.html

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.

[Chong Hou]

Thank you Walter! Could you be more specific? Does the "v0 field" mean the first column of my matrix A?

[Walter Roberson]

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.