bugGNU Octave - Bugs: bug #47560, Eigenvalue order

 
 

bug #47560: Eigenvalue order

Submitted by:  None
Submitted on:  Tue 29 Mar 2016 02:52:29 AM UTC  
 
Category: Octave FunctionSeverity: 1 - Wish
Priority: 3 - LowItem Group: Feature Request
Status: Wont FixAssigned to: None
Originator Name: DeborahOriginator Email: -unavailable-
Open/Closed: ClosedRelease: 3.8.2
Operating System: Any

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Wed 30 Mar 2016 03:30:52 PM UTC, comment #3:

The consensus, both from Octave and Matlab, is that many times there is no need for sorting of the eigenvalues and they may be used as is. It is incorrect, therefore, to penalize these applications by applying an additional sort operation; Particularly because the eigenvector matrix would likewise have to be sorted to match up to the new order of the eigenvalues and that is harder than just sorting a column vector of eigenvalues.

There also exists an easy workaround, which is to call sort() yourself if you need them in a particular order.

Rik <rik5>
Project Administrator
Wed 30 Mar 2016 08:31:49 AM UTC, comment #2:

This is a feature request. The documentation of eig states clear:

"The eigenvalues returned by eig are not ordered."

https://www.gnu.org/software/octave/doc/v4.0.1/Basic-Matrix-Functions.html#Basic-Matrix-Functions

There might be performance reasons for this, as eigenvalues in Octave are computed via BLAS- or Suitesparse-routines. Matlab doen't order them, maybe because of similar reasons, too.

A very quick and uncomplicated way to archive the desired behavior is:

Kai Torben Ohlhus <siko1056>
Project Member
Wed 30 Mar 2016 12:42:56 AM UTC, comment #1:

To Deborah: if all real eigenvalues, sorted in ascending order from -inf to +inf. If all complex, sorted in descending order of absolute value. If mixed, in whatever order it comes out.

Anonymous
Tue 29 Mar 2016 02:52:29 AM UTC, original submission:

Eigenvalues are returned from eig in a mostly random order instead of descending by absolute value. Could this behavior please be changed if possible?

Anonymous

 

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  • -unavailable- added by rik5 (Posted a comment)
  • -unavailable- added by siko1056 (Posted a comment)
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    Follow 7 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Wed 30 Mar 2016 03:30:52 PM UTCrik5Open/ClosedOpen=>Closed
    Wed 30 Mar 2016 08:32:54 AM UTCsiko1056Priority5 - Normal=>3 - Low
    Wed 30 Mar 2016 08:31:49 AM UTCsiko1056CategoryNone=>Octave Function
      Severity3 - Normal=>1 - Wish
      Item GroupNone=>Feature Request
      StatusNone=>Wont Fix
      Operating SystemMicrosoft Windows=>Any

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