expinv (Statistics Toolbox)

Inverse of the exponential cumulative distribution function (cdf)

Syntax

```
X = expinv(P,MU)
```

Description

X = expinv(P,MU) computes the inverse of the exponential cdf with parameters specified by MU for the corresponding probabilities in P. Vector or matrix inputs for P and MU must have the same size. A scalar input is expanded to a constant matrix with the same dimensions as the other input. The parameters in MU must be positive and the values in P must lie on the interval [0 1].

The inverse of the exponential cdf is

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

Examples

Let the lifetime of light bulbs be exponentially distributed with µ = 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 the mean life of the bulbs, then half them will burn out in less than 500 hours.

expfit exppdf