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LGAMMA(3) Linux Programmer's Manual LGAMMA(3)


     lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log
     gamma function


     #include <math.h>
     double lgamma(double x);
     float lgammaf(float x);
     long double lgammal(long double x);
     double lgamma_r(double x, int *signp);
     float lgammaf_r(float x, int *signp);
     long double lgammal_r(long double x, int *signp);
     extern int signgam;
     Link with -lm.
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
     lgammaf(), lgammal():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
     lgamma_r(), lgammaf_r(), lgammal_r():
         /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


     For the definition of the Gamma function, see tgamma(3).
     The lgamma(), lgammaf(), and 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 signgam declared  in
     <math.h>.  It is 1 when the Gamma function is positive or zero, -1 when
     it is negative.
     Since using a constant location signgam is not thread-safe,  the  func-
     tions  lgamma_r(),  lgammaf_r(),  and lgammal_r() have been introduced;
     they return the sign via the argument signp.


     On success, these functions return the natural logarithm of Gamma(x).
     If x is a NaN, a NaN is returned.
     If x is 1 or 2, +0 is returned.
     If x is positive infinity or negative infinity,  positive  infinity  is
     If  x  is a nonpositive integer, a pole error occurs, and the functions
     return +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, respectively.
     If the result overflows, a range error occurs, and the functions return
     HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct math-
     ematical sign.


     See math_error(7) for information on how to determine whether an  error
     has occurred when calling these functions.
     The following errors can occur:
     Pole error: x is a nonpositive integer
            errno  is set to ERANGE (but see BUGS).  A divide-by-zero float-
            ing-point exception (FE_DIVBYZERO) is raised.
     Range error: result overflow
            errno is set to ERANGE.  An  overflow  floating-point  exception
            (FE_OVERFLOW) is raised.


     The   lgamma()  functions  are  specified  in  C99,  POSIX.1-2001,  and
     POSIX.1-2008.  signgam is specified in POSIX.1-2001  and  POSIX.1-2008,
     but  not in C99.  The lgamma_r() functions are nonstandard, but present
     on several other systems.


     In glibc 2.9 and earlier, when a pole error occurs,  errno  is  set  to
     EDOM;  instead of the POSIX-mandated ERANGE.  Since version 2.10, glibc
     does the right thing.




     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
                                2017-09-15                         LGAMMA(3)
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