1LGAMMA(3) Linux Programmer's Manual LGAMMA(3)
2
6 lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log
7 gamma function
8
10 #include <math.h>
11 double lgamma(double x);
13 float lgammaf(float x);
14 long double lgammal(long double x);
15 double lgamma_r(double x, int *signp);
17 float lgammaf_r(float x, int *signp);
18 long double lgammal_r(long double x, int *signp);
19 extern int signgam;
21 Link with -lm.
23 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
25 lgamma():
27 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
28 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
29 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
30 lgammaf(), lgammal():
31 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
32 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
33 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
34 lgamma_r(), lgammaf_r(), lgammal_r():
35 /* Since glibc 2.19: */ _DEFAULT_SOURCE
36 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
37 signgam:
38 _XOPEN_SOURCE
39 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
40 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
41
43 For the definition of the Gamma function, see tgamma(3).
44 The lgamma(), lgammaf(), and lgammal() functions return the natural
46 logarithm of the absolute value of the Gamma function. The sign of the
47 Gamma function is returned in the external integer signgam declared in
48 <math.h>. It is 1 when the Gamma function is positive or zero, -1 when
49 it is negative.
50 Since using a constant location signgam is not thread-safe, the func‐
52 tions lgamma_r(), lgammaf_r(), and lgammal_r() have been introduced;
53 they return the sign via the argument signp.
54
56 On success, these functions return the natural logarithm of Gamma(x).
57 If x is a NaN, a NaN is returned.
59 If x is 1 or 2, +0 is returned.
61 If x is positive infinity or negative infinity, positive infinity is
63 returned.
64 If x is a nonpositive integer, a pole error occurs, and the functions
66 return +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, respectively.
67 If the result overflows, a range error occurs, and the functions return
69 HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct math‐
70 ematical sign.
71
73 See math_error(7) for information on how to determine whether an error
74 has occurred when calling these functions.
75 The following errors can occur:
77 Pole error: x is a nonpositive integer
79 errno is set to ERANGE (but see BUGS). A divide-by-zero float‐
80 ing-point exception (FE_DIVBYZERO) is raised.
81 Range error: result overflow
83 errno is set to ERANGE. An overflow floating-point exception
84 (FE_OVERFLOW) is raised.
85
87 The lgamma() functions are specified in C99, POSIX.1-2001, and
88 POSIX.1-2008. signgam is specified in POSIX.1-2001 and POSIX.1-2008,
89 but not in C99. The lgamma_r() functions are nonstandard, but present
90 on several other systems.
91
93 In glibc 2.9 and earlier, when a pole error occurs, errno is set to
94 EDOM; instead of the POSIX-mandated ERANGE. Since version 2.10, glibc
95 does the right thing.
96
98 tgamma(3)
99
101 This page is part of release 5.10 of the Linux man-pages project. A
102 description of the project, information about reporting bugs, and the
103 latest version of this page, can be found at
104 https://www.kernel.org/doc/man-pages/.
105 2017-09-15 LGAMMA(3)