[Bug math/12144] New: gamma function still returns absurd values

[Bug math/12144] New: gamma function still returns absurd values

[support at transpacific dot net]

http://sourceware.org/bugzilla/show_bug.cgi?id=12144

           Summary: gamma function still returns absurd values
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: critical
          Priority: P2
         Component: math
        AssignedTo: aj@suse.de
        ReportedBy: support@transpacific.net


On Ubuntu 10.04 with latest libm and on older FreeBSD 6.2, gamma() returns bad
values. I see references to this by other people; it has not been addressed.
How serious it is is demonstrated by relating that libm says gamma(2.0) = 0.0
and that gamma(3.0) - 0.39, when both answers should be 1.0. Mathematically
1/gamma(2) is legal but not with this bug. Most statistical modeling is
screwed. I had to migrate to the GSL library to get correct results.

OUCH!

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[Bug math/12144] gamma function still returns absurd values

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12144

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2010-10-21 08:40:00 UTC ---
gamma is a non-standard function that returns $log_e |Γ(x)|$.  Use tgamma for
the gramma function.  And Γ(3) ≠ 1.

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[Bug math/12144] gamma function still returns absurd values

[support at transpacific dot net]

http://sourceware.org/bugzilla/show_bug.cgi?id=12144

--- Comment #2 from Eric Dynamic <support at transpacific dot net> 2010-10-21 19:16:51 UTC ---
Sorry about the 2/3, I meant 1/2. I tried tgamma but it does not exist
in the library on Ubuntu (meaning the latest.) lgamma() of course
returns the error I mention. Therefore there is still no working gamma.

If in libm "gamma" is the function that ought to be named "lngamma" or
"loggamma", then that's an error that should be corrected despite any
"historical precendent" in my opinion.

schwab@linux-m68k.org wrote:
> http://sourceware.org/bugzilla/show_bug.cgi?id=12144
>
> Andreas Schwab <schwab@linux-m68k.org> changed:
>
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|NEW                         |RESOLVED
>          Resolution|                            |INVALID
>
> --- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2010-10-21 08:40:00 UTC ---
> gamma is a non-standard function that returns $log_e |Γ(x)|$.  Use tgamma for
> the gramma function.  And Γ(3) ≠ 1.
>
>

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[Bug math/12144] gamma function still returns absurd values

[pasky at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=12144

Petr Baudis <pasky at suse dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pasky at suse dot cz

--- Comment #3 from Petr Baudis <pasky at suse dot cz> 2010-10-27 02:49:42 UTC ---
If tgamma() truly is not present in Ubuntu's libm (it sure is in Debian's at
least), report that to your distributor.

The gamma() function naming is unfortunate, sadly we cannot reshape the word to
be pretty without any regard to compatibility. I suggest you at least read
through the related Linux manpages which explain the gamma() family of
functions and historical story behind.

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[Bug math/12144] gamma function still returns absurd values

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=12144

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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