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 Suite Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Inaccurate Result
Status:  Confirmed Assigned to:  None
Originator Name:  Open/Closed:  Open
Release:  dev Operating 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
    2018-04-12 rik5 Release4.3.90 => dev
        Summarygammainc fails one test with "upper" flag and complex input => need accurate gammainc algorithm for "large" negative x and small a
    2018-04-11 rik5 Carbon-Copy- => Added m_ginesi

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