1LGAMMA(3) Linux Programmer's Manual LGAMMA(3)
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6 lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log
7 gamma function
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10 #include <math.h>
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12 double lgamma(double x);
13 float lgammaf(float x);
14 long double lgammal(long double x);
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16 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);
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20 extern int signgam;
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22 Link with -lm.
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24 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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26 lgamma(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE ||
27 _ISOC99_SOURCE; or cc -std=c99
28 lgammaf(), lgammal(): _BSD_SOURCE || _SVID_SOURCE ||
29 _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
30 lgamma_r(), lgammaf_r(), lgammal_r(): _BSD_SOURCE || _SVID_SOURCE
31 signgam: _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
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34 For the definition of the Gamma function, see tgamma(3).
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36 The lgamma() function returns the natural logarithm of the absolute
37 value of the Gamma function. The sign of the Gamma function is
38 returned in the external integer signgam declared in <math.h>. It is 1
39 when the Gamma function is positive or zero, -1 when it is negative.
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41 Since using a constant location signgam is not thread-safe, the func‐
42 tions lgamma_r() etc. have been introduced; they return the sign via
43 the argument signp.
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46 On success, these functions return the natural logarithm of Gamma(x).
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48 If x is a NaN, a NaN is returned.
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50 If x is 1 or 2, +0 is returned.
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52 If x is positive infinity or negative infinity, positive infinity is
53 returned.
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55 If x is a non-positive integer, a pole error occurs, and the functions
56 return +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, respectively.
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58 If the result overflows, a range error occurs, and the functions return
59 HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct math‐
60 ematical sign.
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63 See math_error(7) for information on how to determine whether an error
64 has occurred when calling these functions.
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66 The following errors can occur:
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68 Pole error: x is a non-positive integer
69 errno is set to ERANGE (but see BUGS). A divide-by-zero float‐
70 ing-point exception (FE_DIVBYZERO) is raised.
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72 Range error: result overflow
73 errno is set to ERANGE. An overflow floating-point exception
74 (FE_OVERFLOW) is raised.
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77 The lgamma() functions are specified in C99 and POSIX.1-2001. signgam
78 is specified in POSIX.1-2001, but not in C99. The lgamma_r() functions
79 are non-standard, but present on several other systems.
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82 For a pole error, errno is set to EDOM; POSIX.1 says it should be set
83 to ERANGE.
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86 tgamma(3)
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89 This page is part of release 3.22 of the Linux man-pages project. A
90 description of the project, and information about reporting bugs, can
91 be found at http://www.kernel.org/doc/man-pages/.
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95 2008-08-05 LGAMMA(3)