man3/lgamma.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\" Distributed under GPL
   3 .\" based on glibc infopages
   4 .\"
   5 .TH LGAMMA 3 2007-07-26 "" "Linux Programmer's Manual"
   6 .SH NAME
   7 lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam \-
   8 log gamma function
   9 .SH SYNOPSIS
  10 .nf
  11 .B #include <math.h>
  12 .sp
  13 .BI "double lgamma(double " x );
  14 .br
  15 .BI "float lgammaf(float " x );
  16 .br
  17 .BI "long double lgammal(long double " x );
  18 .sp
  19 .BI "double lgamma_r(double " x ", int *" signp );
  20 .br
  21 .BI "float lgammaf_r(float " x ", int *" signp );
  22 .br
  23 .BI "long double lgammal_r(long double " x ", int *" signp );
  24 .br
  25 .BI "extern int " signgam ;
  26 .fi
  27 .sp
  28 Link with \fI\-lm\fP.
  29 .sp
  30 .in -4n
  31 Feature Test Macro Requirements for glibc (see
  32 .BR feature_test_macros (7)):
  33 .in
  34 .sp
  35 .ad l
  36 .BR lgamma (),
  37 .BR lgammaf (),
  38 .BR lgammal ():
  39 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
  40 .I cc\ -std=c99
  41 .br
  42 .BR lgamma_r (),
  43 .BR lgammaf_r (),
  44 .BR lgammal_r ():
  45 _BSD_SOURCE || _SVID_SOURCE
  46 .br
  47 .IR signgam :
  48 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
  49 .ad b
  50 .SH DESCRIPTION
  51 For the definition of the Gamma function, see
  52 .BR tgamma (3).
  53 .PP
  54 The
  55 .BR lgamma ()
  56 function returns the natural logarithm of
  57 the absolute value of the Gamma function.
  58 The sign of the Gamma function is returned in the
  59 external integer \fIsigngam\fP declared in
  60 .IR <math.h> .
  61 It is 1 when the Gamma function is positive or zero, \-1
  62 when it is negative.
  63 .PP
  64 Since using a constant location
  65 .I signgam
  66 is not thread-safe, the functions
  67 .BR lgamma_r ()
  68 etc. have
  69 been introduced; they return this sign via the parameter
  70 .IR signp .
  71 .PP
  72 For non-positive integer values of \fIx\fP,
  73 .BR lgamma ()
  74 returns
  75 .BR HUGE_VAL ,
  76 sets \fIerrno\fP to
  77 .B ERANGE
  78 and raises the zero divide exception.
  79 (Similarly,
  80 .BR lgammaf ()
  81 returns
  82 .B HUGE_VALF
  83 and
  84 .BR lgammal ()
  85 returns
  86 .BR HUGE_VALL .)
  87 .SH ERRORS
  88 In order to check for errors, set
  89 .I errno
  90 to zero and call
  91 .I feclearexcept(FE_ALL_EXCEPT)
  92 before calling these functions.
  93 On return, if
  94 .I errno
  95 is non-zero or
  96 .I fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
  97 is non-zero, an error has occurred.
  98 .LP
  99 A range error occurs if x is too large.
 100 A pole error occurs if x is a negative integer or zero.
 101 .SH "CONFORMING TO"
 102 C99, SVr4, 4.3BSD
 103 .SH "SEE ALSO"
 104 .BR tgamma (3)