# RANEXP Function

Returns a random variate from an exponential distribution.

 Category: Random Number Tip: If you want to change the seed value during execution, you must use the CALL RANEXP routine instead of the RANEXP function.

## Syntax

RANEXP(seed)

### Required Argument

#### seed

is a numeric constant, variable, or expression with an integer value. If seed ≤ 0, the time of day is used to initialize the seed stream.

## Details

The RANEXP function returns a variate that is generated from an exponential distribution with parameter 1. An inverse transform method applied to a RANUNI uniform variate is used.
An exponential variate X with parameter LAMBDA can be generated:
`x=ranexp(seed)/lambda;`
An extreme value variate X with location parameter ALPHA and scale parameter BETA can be generated:
`x=alpha−beta*log(ranexp(seed));`
A geometric variate X with parameter P can be generated as follows:
`x=floor(−ranexp(seed)/log(1−p));`
For a discussion about seeds and streams of data, as well as examples of using the random-number functions, see Generating Multiple Variables from One Seed in Random-Number Functions .

## Comparisons

The CALL RANEXP routine, an alternative to the RANEXP function, gives greater control of the seed and random number streams.