# 3.5.3.1.11 Fcdf

## Description

Computes $F$ cumulative distribution function at f, with parameters ndf, fdf, and tail. The parameters of ndf and fdf must all be positive, and the values in f must be positive. The parameter tail determines the returned probability is the lower tailed or upper tailed.

The result, prob, is the probability that a single observation from a $F$ distribution with parameters ndf and fdf will fall in the interval [0, f] for lower-tailed, [f, $+\infty$] for upper-tailed.

## Syntax

double prob = fcdf(double f, double ndf, double fdf[, int tail])

## Parameters

f

Input, the value of the $F$ variate, $f$. $0\leq f<+\infty$

ndf

Input, the degrees of freedom of the numerator variance, $\nu_1$, must be positive ( $ndf>0.0$ ).

fdf

Input, the degrees of freedom of the denominator variance, $\nu_2$, must be positive ( $fdf>0.0$).

tail

Input, Optional. The tail probability type using for the F distribution
• 1 = the for upper tail probability
• 2 = the lower tail probability (Default if not set)

prob

Output, the returned probability

## Example

fcdf(1000,20,20,1)=; //ANS: 9.0714457299284E-26