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MathGroup Archive 1995

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Sorting eigenvectors by eigenvalue

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg2054] Sorting eigenvectors by eigenvalue
  • From: valentin at wam.umd.edu (William F. Campbell)
  • Date: Mon, 18 Sep 1995 01:50:46 -0400
  • Organization: University of Maryland, College Park

  I'm trying to use Sort to sort eigenvectors by eigenvalue.  The eignevectors
are in a list of lists called vecs, and the eigenvalues in vals after the 
following function call on matrix aa:  

  {vals,vecs}=Eigensystem[aa]

  Then I want to define an ordering function p so I can use Sort[vecs,p].  
I tried the following: 
  
  p[vecs[[i_]],vecs[[j_]]]:=Greater[Abs[vals[[i]],Abs[vals[[j]]]]

  Mathematica wont parse vecs[[i_]] saying that i is neither an integer nor
a list of integers.  How can I accomplish what I want to do?
______________________________________________________________________________
|                                                                            |
|                When endeavoring to explain human behaviour,                |
|                never discount the possibility of stupidity.                |
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|                        Never ascribe to malfeasance                        |
|                  that which can be explained as stupidity.                 |
|                                                                            |
|  Bill Campbell                                                             |
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