chdtr

Chi-square distribution.

SYNOPSIS:

double df, x, y, chdtr();
y = chdtr(df, x);

DESCRIPTION:

Returns the area under the left hand tail (from 0 to x) 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) = igam(v/2.0, x/2.0).

The arguments must both be positive.

ACCURACY:

See igam().

ERROR MESSAGES:

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