chdtrc

Complemented Chi-square distribution.

SYNOPSIS:

double v, x, y, chdtrc();
y = chdtrc(v, x);

DESCRIPTION:

Returns the area under the right hand tail (from x to infinity) of the Chi square probability density function with v degrees of freedom:

                                inf.
                                  -
                      1          | | v/2-1 -t/2
P(x | v)   =   -----------     |   t      e     dt
                  v/2 -       | |
                 2    | (v/2)   -
                                 x

where x is the Chi-square variable.

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

y = chdtr(v, x) = igamc(v/2.0, x/2.0).

The arguments must both be positive.

ACCURACY:

See the igamc() Help topic.

ERROR MESSAGES:

   message         condition      value returned
   domain         x < 0 or v < 1        0.0