| .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de) |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
| .\" <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE) |
| .\" Distributed under GPL |
| .\" %%%LICENSE_END |
| .\" |
| .\" based on glibc infopages |
| .\" |
| .TH LGAMMA 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam \- |
| log gamma function |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .PP |
| .BI "double lgamma(double " x ); |
| .BI "float lgammaf(float " x ); |
| .BI "long double lgammal(long double " x ); |
| .PP |
| .BI "double lgamma_r(double " x ", int *" signp ); |
| .BI "float lgammaf_r(float " x ", int *" signp ); |
| .BI "long double lgammal_r(long double " x ", int *" signp ); |
| .PP |
| .BI "extern int " signgam ; |
| .fi |
| .PP |
| Link with \fI\-lm\fP. |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .nf |
| .BR lgamma (): |
| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .PP |
| .BR lgammaf (), |
| .BR lgammal (): |
| .nf |
| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .PP |
| .BR lgamma_r (), |
| .BR lgammaf_r (), |
| .BR lgammal_r (): |
| .nf |
| /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .PP |
| .IR signgam : |
| .nf |
| _XOPEN_SOURCE |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .SH DESCRIPTION |
| For the definition of the Gamma function, see |
| .BR tgamma (3). |
| .PP |
| The |
| .BR lgamma (), |
| .BR lgammaf (), |
| and |
| .BR lgammal () |
| functions return the natural logarithm of |
| the absolute value of the Gamma function. |
| The sign of the Gamma function is returned in the |
| external integer |
| .I signgam |
| declared in |
| .IR <math.h> . |
| It is 1 when the Gamma function is positive or zero, \-1 |
| when it is negative. |
| .PP |
| Since using a constant location |
| .I signgam |
| is not thread-safe, the functions |
| .BR lgamma_r (), |
| .BR lgammaf_r (), |
| and |
| .BR lgammal_r () |
| have been introduced; they return the sign via the argument |
| .IR signp . |
| .SH RETURN VALUE |
| On success, these functions return the natural logarithm of Gamma(x). |
| .PP |
| If |
| .I x |
| is a NaN, a NaN is returned. |
| .PP |
| If |
| .I x |
| is 1 or 2, +0 is returned. |
| .PP |
| If |
| .I x |
| is positive infinity or negative infinity, |
| positive infinity is returned. |
| .PP |
| If |
| .I x |
| is a nonpositive integer, |
| a pole error occurs, |
| and the functions return |
| .RB + HUGE_VAL , |
| .RB + HUGE_VALF , |
| or |
| .RB + HUGE_VALL , |
| respectively. |
| .PP |
| If the result overflows, |
| a range error occurs, |
| .\" e.g., lgamma(DBL_MAX) |
| and the functions return |
| .BR HUGE_VAL , |
| .BR HUGE_VALF , |
| or |
| .BR HUGE_VALL , |
| respectively, with the correct mathematical sign. |
| .SH ERRORS |
| See |
| .BR math_error (7) |
| for information on how to determine whether an error has occurred |
| when calling these functions. |
| .PP |
| The following errors can occur: |
| .TP |
| Pole error: \fIx\fP is a nonpositive integer |
| .I errno |
| is set to |
| .BR ERANGE |
| (but see BUGS). |
| A divide-by-zero floating-point exception |
| .RB ( FE_DIVBYZERO ) |
| is raised. |
| .TP |
| Range error: result overflow |
| .I errno |
| is set to |
| .BR ERANGE . |
| An overflow floating-point exception |
| .RB ( FE_OVERFLOW ) |
| is raised. |
| .\" glibc (as at 2.8) also supports an inexact |
| .\" exception for various cases. |
| .SH CONFORMING TO |
| The |
| .BR lgamma () |
| functions are specified in C99, POSIX.1-2001, and POSIX.1-2008. |
| .I signgam |
| is specified in POSIX.1-2001 and POSIX.1-2008, but not in C99. |
| The |
| .BR lgamma_r () |
| functions are nonstandard, but present on several other systems. |
| .SH BUGS |
| In glibc 2.9 and earlier, |
| .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6777 |
| when a pole error occurs, |
| .I errno |
| is set to |
| .BR EDOM ; |
| instead of the POSIX-mandated |
| .BR ERANGE . |
| Since version 2.10, glibc does the right thing. |
| .SH SEE ALSO |
| .BR tgamma (3) |