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Linux 2.6 - man page for lgamma (linux section 3posix)

LGAMMA(P)			    POSIX Programmer's Manual				LGAMMA(P)

NAME
       lgamma, lgammaf, lgammal - log gamma function

SYNOPSIS
       #include <math.h>

       double lgamma(double x);
       float lgammaf(float x);
       long double lgammal(long double x);

       extern int signgam;

DESCRIPTION
       These functions shall compute

       The  argument  x  need  not be a non-positive integer (Gamma(x) is defined over the reals,
       except the non-positive integers).

       The sign of Gamma(x) is returned in the external integer signgam.

       These functions need not be reentrant. A function that is not required to be reentrant  is
       not required to be thread-safe.

       An  application	wishing  to  check for error situations should set errno to zero and call
       feclearexcept(FE_ALL_EXCEPT) before calling these functions.  On return, if errno is  non-
       zero  or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,
       an error has occurred.

RETURN VALUE
       Upon successful completion, these functions shall return the logarithmic gamma of x.

       If x is a non-positive integer, a pole error shall  occur  and  lgamma(),  lgammaf(),  and
       lgammal() shall return +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively.

       If  the	correct value would cause overflow, a range error shall occur and lgamma(), lgam-
       maf(), and lgammal() shall return +-HUGE_VAL, +-HUGE_VALF,  and	+-HUGE_VALL  (having  the
       same sign as the correct value), respectively.

       If x is NaN, a NaN shall be returned.

       If x is 1 or 2, +0 shall be returned.

       If x is +-Inf, +Inf shall be returned.

ERRORS
       These functions shall fail if:

       Pole Error
	      The x argument is a negative integer or zero.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set to [ERANGE]. If the integer expression (math_errhandling  &	MATH_ERREXCEPT)  is  non-
       zero, then the divide-by-zero floating-point exception shall be raised.

       Range Error
	      The result overflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set to [ERANGE]. If the integer expression (math_errhandling  &	MATH_ERREXCEPT)  is  non-
       zero, then the overflow floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On  error,  the	expressions  (math_errhandling	&  MATH_ERRNO)	and  (math_errhandling	&
       MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       exp() , feclearexcept() , fetestexcept() ,  isnan()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001,  Section  4.18, Treatment of Error Conditions for Mathematical Func-
       tions, <math.h>

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					LGAMMA(P)


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