Routines (alphabetical) > Routines: F > F_PDF

# F_PDF

The F_PDF function computes cumulative distribution function for an F distribution with defined degrees of freedom in the numerator and denominator. This is the probability P that, in an F distribution, a random variable X is less than or equal to a user-specified cutoff value V.

This routine is written in the IDL language. Its source code can be found in the file `f_pdf.pro` in the `lib` subdirectory of the IDL distribution.

## Examples

Use the following command to compute the probability that a random variable X, from the F distribution with five degrees of freedom in the numerator and 24 degrees of freedom in the denominator, is less than or equal to 3.90. The result should be 0.990059:

PRINT, F_PDF(3.90, 5, 24)

## Syntax

Result = F_PDF(V, Dfn, Dfd)

## Return Value

If all arguments are scalar, the function returns a scalar. If all arguments are arrays, the function matches up the corresponding elements of V, Dfn, and Dfd, returning an array with the same dimensions as the smallest array. If one argument is a scalar and the other arguments are arrays, the function uses the scalar value with each element of the arrays, and returns an array with the same dimensions as the smallest input array.

If any of the arguments are double-precision, the result is double-precision, otherwise the result is single-precision.

## Arguments

### V

A scalar or array that specifies the cutoff value(s).

### Dfn

A positive scalar or array that specifies the number of degrees of freedom of the F distribution numerator.

### Dfd

A positive scalar or array that specifies the number of degrees of freedom of the F distribution denominator.

## Keywords

None.

## Version History

4.0 | Introduced

## See Also

BINOMIAL, CHISQR_PDF, F_CVF, GAUSS_PDF, T_PDF