Cumulative distribution function¶

fdtr
(df1, df2, x)¶ Returns the area from zero to x under the F density function (also known as Snedcor’s density or the variance ratio density).
Parameters:
Description¶
This is the density of x = (u1/df1)/(u2/df2), where u1 and u2 are random variables having Chi square distributions with df1 and df2 degrees of freedom, respectively.
The incomplete beta integral is used according to the formula:
P(x) = incbet(df1/2, df2/2, (df1 * x/(df2 + df1*x))
The arguments a and b are greater than zero, and x is nonnegative.
Accuracy¶
Tested at random points (a, b, x).
x  a, b  relative error  

arithmetic  domain  domain  # trials  peak  rms 
IEEE  0, 1  0, 100  100000  9.8e15  1.7e15 
IEEE  1, 5  0, 100  100000  6.5e15  3.5e16 
IEEE  0, 1  1, 10000  100000  2.2e11  3.3e12 
IEEE  1, 5  1, 10000  100000  1.1e11  1.7e13 
See also incbet()
.
Error messages¶
message  condition  value returned 

fdtr domain  a<0, b<0, x<0  0 