[Octave-bug-tracker] [bug #31776] gamma for negative integers values

[marco atzeri]

URL:
  <http://savannah.gnu.org/bugs/?31776>

                 Summary: gamma for negative integers values
                 Project: GNU Octave
            Submitted by: matzeri
            Submitted on: Fri 26 Nov 2010 03:10:51 PM GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Microsoft Windows

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Details:

>From Mathematical point gamma(-1) should be Inf 
as gamma(0). Matlab provides  gamma(-1)=Inf
The same for the other integer negative values.

The test is expecting NaN as on same systems 
  tgamma(-n)=NaN 
as the NaN value is allowed on 
http://www.opengroup.org/onlinepubs/009695399/functions/tgamma.html

The test fails on system were tgamma(-1)=Inf

---------------------------------------------
>>>>> processing /pub/hg/octave/src/mappers.cc
  ***** test
 x = [-1, 0, 1, Inf];
 v = [NaN, Inf, 1, Inf];
 assert (gamma(x), v);
 assert (gamma(single (x)), single (v));
!!!!! test failed
assert (gamma (x),v) expected
   NaN   Inf     1   Inf
but got
   Inf   Inf     1   Inf
NaNs don't match
-----------------------------------------------

The attached patch provides
  gamma(-n)=Inf 
for all systems and amends test expectation


Reference
http://en.wikipedia.org/wiki/Gamma_function

discussed:
https://www-old.cae.wisc.edu/pipermail/octave-maintainers/2010-October/017501.html

https://www-old.cae.wisc.edu/pipermail/octave-maintainers/2010-November/017796.html




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File Attachments:


-------------------------------------------------------
Date: Fri 26 Nov 2010 03:10:51 PM GMT  Name: changeset_gamma.patch  Size: 2kB
  By: matzeri

<http://savannah.gnu.org/bugs/download.php?file_id=22129>

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