GAMMADIST function

Returns the gamma distribution


 * Usage: GAMMADIST(x,alpha,beta,cumulative)
 * X - The value at which you want to evaluate the distribution.
 * If beta = 1, GAMMADIST returns the standard gamma distribution.
 * If cumulative is TRUE, GAMMADIST returns the cumulative distribution function; if FALSE, it returns the probability density function.
 * If x, alpha, or beta is nonnumeric, GAMMADIST returns the #VALUE! error value.
 * If x < 0, GAMMADIST returns the #NUM! error value.
 * If alpha ≤ 0 or if beta ≤ 0, GAMMADIST returns the #NUM! error value.
 * For a positive integer n, when alpha = n/2, beta = 2, and cumulative = TRUE, GAMMADIST returns (1 - CHIDIST(x)) with n degrees of freedom.
 * When alpha is a positive integer, GAMMADIST is also known as the Erlang distribution.