CHIPR

This function evaluates the chi‑squared probability density function.

Function Return Value

CHIPR — Function value, the value of the probability density function. (Output)

Required Arguments

X — Argument for which the chi‑squared probability density function is to be evaluated. (Input)

DF — Number of degrees of freedom of the chi‑squared distribution. (Input)

FORTRAN 90 Interface

Generic: CHIPR (X, DF)

Specific: The specific interface names are S_CHIPR and D_CHIPR.

FORTRAN 77 Interface

Single: CHIPR (X, DF)

Double: The double precision name is DCHIPR.

Description

The function CHIPR evaluates the chi‑squared probability density function. The chi‑squared distribution is a special case of the gamma distribution and is defined as

 

Example

In this example, we evaluate the probability function at X = 3.0, DF = 5.0.

 

USE UMACH_INT

USE CHIPR_INT

IMPLICIT NONE

INTEGER NOUT

REAL X, DF, PR

CALL UMACH(2, NOUT)

X = 3.0

DF = 5.0

PR = CHIPR(X, DF)

WRITE (NOUT, 99999) X, DF, PR

99999 FORMAT (' CHIPR(', F4.2, ', ', F4.2, ') = ', F6.4)

END

Output

 

CHIPR(3.00, 5.00) = 0.1542