diff options
Diffstat (limited to 'manual/math.texi')
| -rw-r--r-- | manual/math.texi | 29 |
1 files changed, 25 insertions, 4 deletions
diff --git a/manual/math.texi b/manual/math.texi index 4386c2fefc..e1d597d06a 100644 --- a/manual/math.texi +++ b/manual/math.texi @@ -857,7 +857,8 @@ The sign of the gamma function is stored in the global variable the intermediate result was positive or zero, and, @code{-1} if it was negative. -You can compute the actual gamma function as follows: +To compute the real gamma function you can use the @code{tgamma} +function or you can compute the values as follows: @smallexample lgam = lgamma(x); gam = signgam*exp(lgam); @@ -878,15 +879,35 @@ the intermediate result in the variable pointed to by @var{signp} instead of in the @var{signgam} global. @end deftypefun -@ignore @comment math.h @comment SVID @deftypefun double gamma (double @var{x}) @deftypefunx float gammaf (float @var{x}) @deftypefunx {long double} gammal (long double @var{x}) -??? _not_ exp(lgamma())*signgam - historical? +These functions exist for compatibility reasons. They are equivalent to +@code{lgamma} etc. It is better to use @code{lgamma} since for one the +name reflect better the actual computation and @code{lgamma} is also +standardized in @w{ISO C 9x} while @code{gamma} is not. +@end deftypefun + +@comment math.h +@comment XPG +@deftypefun double tgamma (double @var{x}) +@deftypefunx float tgammaf (float @var{x}) +@deftypefunx {long double} tgammal (long double @var{x}) +@code{tgamma} applies the gamma function to @var{x}. The gamma +function is defined as +@tex +$$\Gamma(x) = \int_0^\infty t^{x-1} e^{-t} \hbox{d}t$$ +@end tex +@ifnottex +@smallexample +gamma (x) = integral from 0 to @infinity{} of t^(x-1) e^-t dt +@end smallexample +@end ifnottex + +This function was introduced in @w{ISO C 9x}. @end deftypefun -@end ignore @comment math.h @comment SVID |