gamma — The gamma function.
y = gamma(x)
gamma(x) evaluates the gamma function at all the
elements of x. The gamma function is defined by
:

and generalizes the factorial function for real numbers
(gamma(n+1) = n!).
// simple examples
gamma(0.5)
gamma(6)-prod(1:5)
// the graph of the Gamma function on [a,b]
a = -3; b = 5;
x = linspace(a,b,40000)';
y = gamma(x);
clf()
c=xget("color")
xset("color",2)
plot2d(x, y, style=0, axesflag=5, rect=[a, -10, b, 10])
xset("color",c)
xtitle("The gamma function on ["+string(a)+","+string(b)+"]")
xselect()