man3/gamma.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\"
   3 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
   4 .\" Distributed under GPL
   5 .\" %%%LICENSE_END
   6 .\"
   7 .\" Modified 2003-11-18, aeb: historical remarks
   8 .\"
   9 .TH GAMMA 3 2017-09-15 "GNU" "Linux Programmer's Manual"
  10 .SH NAME
  11 gamma, gammaf, gammal \- (logarithm of the) gamma function
  12 .SH SYNOPSIS
  13 .B #include <math.h>
  14 .PP
  15 .BI "double gamma(double " x ");"
  16 .br
  17 .BI "float gammaf(float " x ");"
  18 .br
  19 .BI "long double gammal(long double " x ");"
  20 .PP
  21 Link with \fI\-lm\fP.
  22 .PP
  23 .in -4n
  24 Feature Test Macro Requirements for glibc (see
  25 .BR feature_test_macros (7)):
  26 .in
  27 .PP
  28 .ad l
  29 .BR gamma ():
  30 .RS 4
  31 _XOPEN_SOURCE
  32     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  33     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  34 .RE
  35 .BR gammaf (),
  36 .BR gammal ():
  37 .RS 4
  38 _XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE)
  39     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  40     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  41 .RE
  42 .ad b
  43 .SH DESCRIPTION
  44 These functions are deprecated: instead, use either the
  45 .BR tgamma (3)
  46 or the
  47 .BR lgamma (3)
  48 functions, as appropriate.
  49 .PP
  50 For the definition of the Gamma function, see
  51 .BR tgamma (3).
  52 .SS *BSD version
  53 The libm in 4.4BSD and some versions of FreeBSD had a
  54 .BR gamma ()
  55 function that computes the Gamma function, as one would expect.
  56 .SS glibc version
  57 Glibc has a
  58 .BR gamma ()
  59 function that is equivalent to
  60 .BR lgamma (3)
  61 and computes the natural logarithm of the Gamma function.
  62 .SH RETURN VALUE
  63 See
  64 .BR lgamma (3).
  65 .SH ERRORS
  66 See
  67 .BR lgamma (3).
  68 .SH ATTRIBUTES
  69 For an explanation of the terms used in this section, see
  70 .BR attributes (7).
  71 .TS
  72 allbox;
  73 lbw27 lb lb
  74 l l l.
  75 Interface       Attribute       Value
  76 T{
  77 .BR gamma (),
  78 .BR gammaf (),
  79 .BR gammal ()
  80 T}      Thread safety   MT-Unsafe race:signgam
  81 .TE
  82 .SH CONFORMING TO
  83 Because of historical variations in behavior across systems,
  84 this function is not specified in any recent standard.
  85 It was documented in SVID 2.
  86 .SH NOTES
  87 .SS History
  88 4.2BSD had a
  89 .BR gamma ()
  90 that computed
  91 .RI ln(|Gamma(| x |)|),
  92 leaving the sign of
  93 .RI Gamma(| x |)
  94 in the external integer
  95 .IR signgam .
  96 In 4.3BSD the name was changed to
  97 .BR lgamma (3),
  98 and the man page promises
  99 .PP
 100 .in +4n
 101 "At some time in the future the name gamma will be rehabilitated
 102 and used for the Gamma function"
 103 .in
 104 .PP
 105 This did indeed happen in 4.4BSD, where
 106 .BR gamma ()
 107 computes the Gamma function (with no effect on
 108 .IR signgam ).
 109 However, this came too late, and we now have
 110 .BR tgamma (3),
 111 the "true gamma" function.
 112 .\" The FreeBSD man page says about gamma() that it is like lgamma()
 113 .\" except that is does not set signgam.
 114 .\" Also, that 4.4BSD has a gamma() that computes the true gamma function.
 115 .SH SEE ALSO
 116 .BR lgamma (3),
 117 .BR signgam (3),
 118 .BR tgamma (3)