Computes
the (numerical) integral of the (1-parameter) gamma distribution
by the Simpson's rule.
The 1-parameter gamma distribution is
f(x; α) =
1 ⁄ Γ(α)
xα−1
exp(−x) . It is:
γ2(x; α, β) =
γ1(x ⁄ β;
α) ⁄ β .
Also, Γ2(x; α, β) =
Γ1(x ⁄ β; α) .
(The presence of the gamma function,
though used as its LN, may cause overflows for high values
of α .)
Draws plots of f (permitting, e.g.,
to verify the mode) and F. | 
