expinv (Statistics Toolbox)

Inverse of the exponential cumulative distribution function (cdf).

Syntax

X = expinv(P,MU)

Description

expinv(P,MU) computes the inverse of the exponential cdf with parameter MU for the probabilities in P. The arguments P and MU must be the same size except that a scalar argument functions as a constant matrix of the size of the other argument.

The parameter MU must be positive and P must lie on the interval [0 1].

The inverse of the exponential cdf is:

The result, x, is the value such that the probability is p that an observation from an exponential distribution with parameter µ will fall in the range [0 x].

Examples

Let the lifetime of light bulbs be exponentially distributed with mu equal to 700 hours. What is the median lifetime of a bulb?

expinv(0.50,700)

ans =

  485.2030

So, suppose you buy a box of "700 hour" light bulbs. If 700 hours is mean life of the bulbs, then half them will burn out in less than 500 hours.

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