lyngby_pdf_f - F probability density function
function P = lyngby_pdf_f(x, r1, r2)
Input: x Value where the function is evaluated
r1 Numerator degrees of freedom
r2 Denominator degrees of freedom
Output: p Probability density funtion
This function returns the probability density function for
Fisher's F-distribution. The function is zero for negative x,
and an error is returned if it is called with negative
values.
See also: lyngby_cdf_f, lyngby_cdf_gauss