gamcdf (Statistics Toolbox)

Gamma cumulative distribution function (cdf).

Syntax

P = gamcdf(X,A,B)

Description

gamcdf(X,A,B) computes the gamma cdf with parameters A and B at the values in X. The arguments X, A, and B must all be the same size except that scalar arguments function as constant matrices of the common size of the other arguments.

Parameters A and B are positive.

The gamma cdf is:

The result, p, is the probability that a single observation from a gamma distribution with parameters a and b will fall in the interval [0 x].

gammainc is the gamma distribution with a single parameter, a, with b at its default value of 1.

Examples

a = 1:6;
b = 5:10;
prob = gamcdf(a.*b,a,b)

prob =

    0.6321    0.5940    0.5768    0.5665    0.5595    0.5543

The mean of the gamma distribution is the product of the parameters, a*b. In this example as the mean increases, it approaches the median (i.e., the distribution gets more symmetric).

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