bugGNU Octave - Bugs: bug #45146, chol: document behavior with...

 
 

bug #45146: chol: document behavior with non-hermitian complex inputs

Submitted by:  None
Submitted on:  Tue 19 May 2015 11:15:27 PM UTC  
 
Category: DocumentationSeverity: 2 - Minor
Priority: 3 - LowItem Group: Documentation
Status: FixedAssigned to: None
Originator Name: Nathan WhiteheadOriginator Email: -unavailable-
Open/Closed: ClosedRelease: dev
Operating System: Any

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Mon 09 May 2016 10:58:28 AM UTC, comment #3:

Your patch was merged within the renewal of the documentation.

http://hg.savannah.gnu.org/hgweb/octave/rev/54fa4dcba730

Kai Torben Ohlhus <siko1056>
Project Member
Wed 03 Jun 2015 11:53:34 PM UTC, comment #2:

The patch looks good as far as Texinfo formatting goes. The added text, though, doesn't explain the effect of the "lower" string options that can be passed to the chol function.

Can you take a look at simply adding on to the last paragraph in the existing docstring that already tries to explain what this is doing:

> For full matrices, if the @qcode{"lower"} flag is set only the lower
> triangular part of the matrix is used for the factorization, otherwise the
> upper triangular part is used.


This is attempting to describe the behavior in question, so it would be best to just expand or reword this paragraph to improve it, and move it elsewhere in the text if you think it works better somewhere else.

Thanks.

Mike Miller <mtmiller>
Project Administrator
Wed 20 May 2015 12:56:13 AM UTC, comment #1:

Thanks for your bug report. Confirmed, this is not documented properly in the help text for chol. Can you provide a patch for the docstring?

Mike Miller <mtmiller>
Project Administrator
Tue 19 May 2015 11:15:27 PM UTC, original submission:

The chol() function silently succeeds with non-intuitive results in the case where the input matrix is complex and non-hermitian.

The documentation states that the function fails if the input is not positive definite, or that chol(A)' * chol(A) = A if it is positive definite. For the case where A is complex but not hermitian, the function succeeds and returns a value that does not satisfy chol(A)' * chol(A) = A.

For this code I would expect either an error or a result that is close to machine epsilon. I actually get the result:

I believe the function is only looking at the upper triangular part and assuming the lower triangular part is conjugate transpose; this should be included in the documentation for the function.

Anonymous

 

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Attached Files
file #34075:  choldoc.diff added by None (1KiB - text/x-patch - Attached is an attempt at a patch.)

 

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Items that depend on this one: None found

 

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  • -unavailable- added by siko1056 (Posted a comment)
  • -unavailable- added by mtmiller (Posted a comment)
  • -unavailable- added by None (Submitted the item)
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    Follow 12 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Mon 09 May 2016 10:58:28 AM UTCsiko1056StatusNeed Info=>Fixed
      Open/ClosedOpen=>Closed
    Mon 09 May 2016 09:19:40 AM UTCsiko1056Dependencies-=>Depends on bugs #44313
    Wed 03 Jun 2015 11:53:34 PM UTCmtmillerStatusPatch Submitted=>Need Info
    Fri 22 May 2015 01:44:26 AM UTCmtmillerStatusConfirmed=>Patch Submitted
    Thu 21 May 2015 05:15:20 PM UTCNoneAttached File-=>Added choldoc.diff, #34075
    Wed 20 May 2015 12:56:13 AM UTCmtmillerSeverity3 - Normal=>2 - Minor
      Priority5 - Normal=>3 - Low
      StatusNone=>Confirmed
      Release3.8.1=>dev
      Operating SystemGNU/Linux=>Any
      Summarychol succeeds with incorrect factorization on non-hermitian complex inputs=>chol: document behavior with non-hermitian complex inputs

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