Noncentral F Distribution

The distribution of $\left(X_1/X_2\right)\left({\nu }_2/{\nu }_1\right)$ if $X_1$ is non-central chi-squared with ${\nu }_1$ degrees of freedom and parameter $\lambda$, and $X_2$ is chi-squared with ${\nu }_2$ degrees of freedom.

There are 3 shape parameters: the degrees of freedom ${\nu }_1>0$ and ${\nu }_2>0$; and $\lambda \ge 0$.