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MathGroup Archive 2008

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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.


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