• To: mathgroup at smc.vnet.net
• Subject: [mg90917] Re: question about sorting lists
• From: Ray Koopman <koopman at sfu.ca>
• Date: Tue, 29 Jul 2008 06:10:05 -0400 (EDT)
• References: <g6h5ec\$h1f\$1@smc.vnet.net>

```On Jul 26, 11:43 pm, Tatyana Polenova <tpole... at mail.chem.udel.edu>
wrote:
> Indeed, I forgot to specify that the eigenvalues have to also
> be arranged in order of increasing or decreasing their values
> depending on what the distance is between the adjacent two.
> Say, the eigenvalues list is {-2, 1, -3}. The way this list
> needs to be ordered is {-3, -2, 1}. If the list is {1, 2, -3}
> then it needs to be ordered as {2, 1, -3}. So that the middle
> element in the list has an intermediate absolute value, and
> the distance between the second and the third elements in the
> list is the largest.

Transpose @ If[#[[2,1]]<.5(#[[1,1]]+#[[3,1]]),@,Reverse@#]& @ Sort @
Transpose @ Eigensystem @ yourmatrix

```

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