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Section: Mathematical Functions
Computes the gamma function for real arguments. The gamma function takes only a single argument 
y = gamma(x)
 where x is either a float or double array. The output vector y is the same size (and type) as x. 
The gamma function is defined by the integral:
![\[ \Gamma(x) = \int_{0}^{\infty} e^{-t} t^{x-1} \, dt \]](form_74.png) 
The gamma function obeys the interesting relationship
![\[ \Gamma(x) = (x-1)\Gamma(x-1), \]](form_75.png) 
and for integer arguments, is equivalent to the factorial function.
Here is a plot of the gamma function over the range [-5,5].
--> x = linspace(-5,5);
--> y = gamma(x);
--> plot(x,y); xlabel('x'); ylabel('gamma(x)');
--> axis([-5,5,-5,5]);
which results in the following plot.
