geoinv (Statistics Toolbox)

Inverse of the geometric cumulative distribution function (cdf).

Syntax

X = geoinv(Y,P)

Description

X = geoinv(Y,P) returns the smallest positive integer X such that the geometric cdf evaluated at X is equal to or exceeds Y. You can think of Y as the probability of observing X successes in a row in independent trials where P is the probability of success in each trial.

Vector or matrix inputs for P and Y must have the same size, which is also the size of X. A scalar input for P and Y is expanded to a constant matrix with the same dimensions as the other input. The values in P and Y must lie on the interval [0 1].

Examples

The probability of correctly guessing the result of 10 coin tosses in a row is less than 0.001 (unless the coin is not fair).

psychic = geoinv(0.999,0.5)

psychic =

     9

The example below shows the inverse method for generating random numbers from the geometric distribution.

rndgeo = geoinv(rand(2,5),0.5)

rndgeo =

     0     1     3     1     0
     0     1     0     2     0

geocdf geomean