gdtr

Gamma distribution function.

SYNOPSIS:

double a, b, x, y, gdtr();
y = gdtr(a, b, x);

DESCRIPTION:

Returns the integral from zero to x of the gamma probability density function:

                x
        b       -
       a       | |   b-1 -at
y = -----    |    t    e    dt
       -     | |
      | (b)   -
               0

The incomplete gamma integral is used, according to the relation:

y = igam(b, ax).

ACCURACY:

See the igam() Help topic.

ERROR MESSAGES:

message      condition      value returned
domain         x < 0            0.0