The f-ratio random variable is a continuous probability random variable with probability density function given by:

subject to the following conditions:

The FRatio variate is related to independent ChiSquare variates with degrees of freedom nu and omega by the formula FRatio(nu,omega) ~ (ChiSquare(nu)*omega)/(ChiSquare(omega)*nu)

$\mathrm{with}\left(\mathrm{Student}\left[\mathrm{Statistics}\right]\right)\:$

$X≔\mathrm{FRatioRandomVariable}\left(\mathrm{\nu }\,\mathrm{\omega }\right)\:$

$\mathrm{PDF}\left(X\,u\right)$

$\left\{\begin{array}{cc}0& u<0\\ \frac{\mathrm{\Gamma }\left(\frac{\mathrm{\nu }}{2}+\frac{\mathrm{\omega }}{2}\right){\left(\frac{\mathrm{\nu }}{\mathrm{\omega }}\right)}^{\frac{\mathrm{\nu }}{2}}{u}^{\frac{\mathrm{\nu }}{2}-1}}{\mathrm{\Gamma }\left(\frac{\mathrm{\nu }}{2}\right)\mathrm{\Gamma }\left(\frac{\mathrm{\omega }}{2}\right){\left(1+\frac{\mathrm{\nu }u}{\mathrm{\omega }}\right)}^{\frac{\mathrm{\nu }}{2}+\frac{\mathrm{\omega }}{2}}}& \mathrm{otherwise}\end{array}\right.$

$\mathrm{PDF}\left(X\&comma;0.5\right)$

$\frac{\mathrm{\Gamma }\left(0.5000000000\mathrm{\nu }+0.5000000000\mathrm{\omega }\right){\left(\frac{\mathrm{\nu }}{\mathrm{\omega }}\right)}^{0.5000000000\mathrm{\nu }}{0.5}^{0.5000000000\mathrm{\nu }-1.}}{\mathrm{\Gamma }\left(0.5000000000\mathrm{\nu }\right)\mathrm{\Gamma }\left(0.5000000000\mathrm{\omega }\right){\left(1.+\frac{0.5\mathrm{\nu }}{\mathrm{\omega }}\right)}^{0.5000000000\mathrm{\nu }+0.5000000000\mathrm{\omega }}}$

$\mathrm{Mean}\left(X\right)$

$\left\{\begin{array}{cc}\mathrm{undefined}& \mathrm{\omega }\le 2\\ \frac{\mathrm{\omega }}{\mathrm{\omega }-2}& \mathrm{otherwise}\end{array}\right.$

$\mathrm{Variance}\left(X\right)$

$\left\{\begin{array}{cc}\mathrm{undefined}& \mathrm{\omega }\le 4\\ \frac{2{\mathrm{\omega }}^2\left(\mathrm{\nu }+\mathrm{\omega }-2\right)}{\mathrm{\nu }{\left(\mathrm{\omega }-2\right)}^2\left(\mathrm{\omega }-4\right)}& \mathrm{otherwise}\end{array}\right.$

$Y≔\mathrm{FRatioRandomVariable}\left(7\&comma;8\right)\&colon;$

$\mathrm{PDF}\left(Y\&comma;x\&comma;\mathrm{output}=\mathrm{plot}\right)$

$\mathrm{CDF}\left(Y\&comma;x\right)$

$\left\{\begin{array}{cc}0& x\le 0\\ \frac{343x^{\raisebox{1ex}{$7$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\sqrt{7}\left(343x^3+2548x^2+8008x+13728\right)}{{\left(8+7x\right)}^{\raisebox{1ex}{$13$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}& 0<x\end{array}\right.$

$\mathrm{CDF}\left(Y\&comma;3\&comma;\mathrm{output}=\mathrm{plot}\right)$

Evans, Merran; Hastings, Nicholas; and Peacock, Brian. Statistical Distributions. 3rd ed. Hoboken: Wiley, 2000.

Johnson, Norman L.; Kotz, Samuel; and Balakrishnan, N. Continuous Univariate Distributions. 2nd ed. 2 vols. Hoboken: Wiley, 1995.

Stuart, Alan, and Ord, Keith. Kendall's Advanced Theory of Statistics. 6th ed. London: Edward Arnold, 1998. Vol. 1: Distribution Theory.

The Student[Statistics][FRatioRandomVariable] command was introduced in Maple 18.

For more information on Maple 18 changes, see Updates in Maple 18.