bugGNU Octave - Bugs: bug #53612, need accurate gammainc algorithm...


bug #53612: need accurate gammainc algorithm for "large" negative x and small a

Submitted by:  Rik <rik5>
Submitted on:  Wed 11 Apr 2018 06:22:53 PM UTC  
Category: Test SuiteSeverity: 3 - Normal
Priority: 5 - NormalItem Group: Inaccurate Result
Status: ConfirmedAssigned to: None
Originator Name: Open/Closed: Open
Release: devOperating System: Any

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Thu 12 Apr 2018 03:37:07 PM UTC, comment #2:

Thanks for the insight. I've re-titled the bug report to reflect that we really just need a better algorithm.

Rik <rik5>
Project Administrator
Thu 12 Apr 2018 07:47:52 AM UTC, comment #1:

Dear Rik,

gammainc is quite inaccurate when x is a "large" negative and a is small. Unfortunately I was not able to find an efficient numerical expansion for such values. I put that test in the hope that someone will be able to fix it.

Michele Ginesi <m_ginesi>
Wed 11 Apr 2018 06:22:53 PM UTC, original submission:

The following test is failing

On my system, the result is

I don't know if the tolerance should be relaxed, or the algorithm within gammainc should be improved.

Rik <rik5>
Project Administrator


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    Follow 3 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Thu 12 Apr 2018 03:37:07 PM UTCrik5Release4.3.90=>dev
      Summarygammainc fails one test with "upper" flag and complex input=>need accurate gammainc algorithm for "large" negative x and small a
    Wed 11 Apr 2018 06:49:50 PM UTCrik5Carbon-Copy-=>Added m_ginesi

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