Eigenvalues Okay, Eigenvectors Fail

*To*: mathgroup at smc.vnet.net*Subject*: [mg88096] Eigenvalues Okay, Eigenvectors Fail*From*: jfuite at phys.ualberta.ca*Date*: Thu, 24 Apr 2008 05:58:36 -0400 (EDT)

Dear Mathematica Adepts, I seek the eigenvectors and corresponding eigenvalues of a large matrix of real values, m, such that, Union[Head /@ Flatten[m]]] = {Real}. So far I have no trouble with this for matrices up to n x n, n > 1300 using the function Eigensystem with very fast results. But, sometimes, when I analyze transformed submatrices (mSub) of my original matrix, where n' < 1300, the function, Eigensystem, fails to produce output. Further, Eigenvalues[mSub], quickly produces a valid list of n' eigenvalues, but, Eigenvectors[mSub] fails to complete. Therefore I ask, "What is happening such that I can calculate a complete list of n' eigenvalues for a real matrix, mSub, but I cannot calculate the corresponding eigenvectors?" I appreciate any thoughts on this. I use Mathematica 5.1.0.0 on MacOS X 10.5.2.