# How to use the EXPONDIST function

**What is the EXPONDIST function?**

The EXPONDIST function calculates the exponential distribution representing an outcome in the form of probability.

This function is in the compatibility category and has been replaced by the EXPON.DIST function which was introduced in Excel 2010.

**What is an exponential distribution?**

The exponential distribution is a continuous probability distribution that models the time between events in a Poisson point process. It is characterized by a constant hazard rate so that the conditional probability of an event does not depend on how much time has passed already.

**What is a hazard rate?**

The hazard rate is the conditional probability that an event will occur in a small interval given it has not yet occurred. It is often assumed constant in Poisson processes and given by the exponential distribution's parameter.

**What is a Poisson point process?**

A Poisson point process is a random collection of points representing events in time or space that follow a Poisson distribution. It has independence between points and a constant rate of average occurrence over any interval.

**What is a Poisson distribution?**

The Poisson distribution is a discrete probability distribution that models the number of events occurring in a fixed interval of time or space. The events must be independent and their average rate is known and constant.

**What is independence between points?**

Independence between points means that the position or timing of one point in a stochastic spatial or temporal point process does not affect or influence the probability distribution governing the other points. In other words, it is completely random.

**What is a stochastic spatial process?**

A stochastic spatial process is a random mechanism for generating points distributed in space according to some probability distribution and spatial relationship between the points.

**What is a temporal point process?**

A temporal point process generates random events in time such as the arrival of customers or radioactive decay with certain probabilistic properties concerning the timing and intervals between events.

**What is memorylessness?**

Memorylessness is the property of certain probability distributions like the exponential and geometric where past outcomes do not affect future ones, so the conditional probability stays constant regardless of history.

**What is a probability distribution?**

A probability distribution lets you analyze how likely different random values occurs, in other words, it shows how often we would expect to see different potential values.

**What is a continuous probability distribution?**

A continuous probability distribution is defined over an interval and range of continuous values, giving the probability an outcome is exactly equal to any value, and having an area under its probability density curve equal to 1.

## EXPONDIST Function Syntax

EXPONDIST(*x,lambda,cumulative*)

## EXPONDIST Function Arguments

x |
Required. |

lambda |
Required. |

cumulative |
Required. A boolean value. TRUE - cumulative distribution function FALSE - probability density function |

## EXPONDIST Function Example

Formula in cell C7:

## EXPONDIST Function not working

The EXPONDIST function returns

- #VALUE! error value if
*lambda*or*x*is non-numeric. - #NUM! error value if:
- x < 0 (zero)
- lambda <= 0 (zero)

## How is the EXPONDIST Function calculated?

The general equation to calculate the cumulative distribution function:

The general equation to calculate the probability density distribution:

### Functions in 'Compatibility' category

The EXPONDIST function function is one of 21 functions in the 'Compatibility' category.

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