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OpenSolaris 2009.06 - man page for lgamma (opensolaris section 3m)

lgamma(3M)						  Mathematical Library Functions						lgamma(3M)

NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, gamma, gammaf, gammal, gamma_r, gammaf_r, gammal_r - log gamma function
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ] #include <math.h> extern int signgam; double lgamma(double x); float lgammaf(float x); long double lgammal(long double x); double gamma(double x); float gammaf(float x); long double gammal(long double x); double lgamma_r(double x, int *signgamp); float lgammaf_r(float x, int *signgamp); long double lgammal_r(long double x, int *signgamp); double gamma_r(double x, int *signgamp); float gammaf_r(float x, int *signgamp); long double gammal_r(long double x, int *signgamp);
DESCRIPTION
These functions return ln||~(x)| where |~(x) = integral from 0 to +Infinity of pow(t,x-1)*exp(-t) dt for x > 0 and |~(x) = n/(|~(1-x)sin(nx)) for x < 1. These functions use the external integer signgam to return the sign of |~(x) while lgamma_r() and gamma_r() use the user-allocated space addressed by signgamp.
RETURN VALUES
Upon successful completion, these functions return the logarithmic gamma of x. If x is a non-positive integer, a pole error occurs and these functions return +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively. If x is NaN, a NaN is returned. If x is 1 or 2, +0 shall be returned. If x is +-Inf, +Inf is returned.
ERRORS
These functions will fail if: Pole Error The x argument is a negative integer or 0. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised.
USAGE
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions. In the case of lgamma(), do not use the expression signgam*exp(lgamma(x)) to compute `g := |~(x)' Instead compute lgamma() first: lg = lgamma(x); g = signgam*exp(lg); only after lgamma() has returned can signgam be correct. Note that |~(x) must overflow when x is large enough, underflow when -x is large enough, and generate a division by 0 exception at the singularities x a nonpositive integer.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |See below. | +-----------------------------+-----------------------------+ |MT-Level |See below. | +-----------------------------+-----------------------------+ The lgamma(), lgammaf(), lgammal(), and gamma() functions are Standard. The lgamma_r(), lgammaf_r(), lgammal_r(), gamma_r(), gammaf_r(), and gammal_r(), functions are Stable. The lgamma(), lgammaf(), lgammal(), gamma(), gammaf(), and gammal() functions are Unsafe in multithreaded applications. The lgamma_r(), lgammaf_r(), lgammal_r(), gamma_r(), gammaf_r(), and gammal_r() functions are MT-Safe and should be used instead.
SEE ALSO
exp(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), math.h(3HEAD), attributes(5), standards(5)
NOTES
When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in mul- tithreaded applications. SunOS 5.11 12 Jul 2006 lgamma(3M)

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