gamma(3) - f39

1gamma(3)                   Library Functions Manual                   gamma(3)
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NAME

6       gamma, gammaf, gammal - (logarithm of the) gamma function
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LIBRARY

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       [[deprecated]] double gamma(double x);
15       [[deprecated]] float gammaf(float x);
16       [[deprecated]] long double gammal(long double x);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       gamma():
21           _XOPEN_SOURCE
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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25       gammaf(), gammal():
26           _XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE)
27               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
28               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

31       These  functions  are  deprecated: instead, use either the tgamma(3) or
32       the lgamma(3) functions, as appropriate.
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34       For the definition of the Gamma function, see tgamma(3).
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36   *BSD version
37       The libm in 4.4BSD and some versions of FreeBSD had a gamma()  function
38       that computes the Gamma function, as one would expect.
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40   glibc version
41       glibc  has  a gamma() function that is equivalent to lgamma(3) and com‐
42       putes the natural logarithm of the Gamma function.
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RETURN VALUE

45       See lgamma(3).
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ERRORS

48       See lgamma(3).
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ATTRIBUTES

51       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
52       tributes(7).
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54       ┌─────────────────────────────┬───────────────┬────────────────────────┐
55       │Interface                    │ Attribute     │ Value                  │
56       ├─────────────────────────────┼───────────────┼────────────────────────┤
57       │gamma(), gammaf(), gammal()  │ Thread safety │ MT-Unsafe race:signgam │
58       └─────────────────────────────┴───────────────┴────────────────────────┘
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STANDARDS

61       None.
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HISTORY

64       SVID 2.
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66       Because  of  historical  variations  in  behavior  across systems, this
67       function is not specified in any recent standard.
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69       4.2BSD had a gamma() that computed ln(|Gamma(|x|)|), leaving  the  sign
70       of  Gamma(|x|) in the external integer signgam.  In 4.3BSD the name was
71       changed to lgamma(3), and the man page promises
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73           "At some time in the future the name gamma  will  be  rehabilitated
74           and used for the Gamma function"
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76       This  did  indeed  happen  in  4.4BSD, where gamma() computes the Gamma
77       function (with no effect on signgam).  However, this came too late, and
78       we now have tgamma(3), the "true gamma" function.
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