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TGAMMA(3)		   Linux Programmers Manual		    TGAMMA(3)

       tgamma, tgammaf, tgammal - true gamma function


       double tgamma(double x);
       float tgammaf(float x);
       long double tgammal(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       tgamma(), tgammaf(), tgammal(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE;
       or cc -std=c99

       The Gamma function is defined by

	Gamma(x) = integral from 0 to infinity of t^(x-1) e^-t dt

       It is defined for every real number except for  non-positive  integers.
       For non-negative integral m one has

	Gamma(m+1) = m!

       and, more generally, for all x:

	Gamma(x+1) = x * Gamma(x)

       Furthermore,  the  following  is  valid for all values of x outside the

	Gamma(x) * Gamma(1 - x) = PI / sin(PI * x)

       This function returns the value of the Gamma function for the  argument
       x.   It had to be called "true gamma function" since there is already a
       function gamma(3) that returns something else.

       In order to check for errors, set errno to  zero  and  call  feclearex
       cept(FE_ALL_EXCEPT)  before  calling  these  functions.	 On return, if
       errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO |  FE_OVER
       FLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

       A  range  error	occurs if x is too large.  A pole error occurs if x is
       zero.  A domain error (or a pole error) occurs if x is a negative inte


       gamma(3), lgamma(3)

       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2007-07-26			     TGAMMA(3)

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