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# prob.ExponentialDistribution class

Package: prob
Superclasses: prob.ToolboxFittableParametricDistribution

Exponential probability distribution object

## Description

prob.ExponentialDistribution is an object consisting of parameters, a model description, and sample data for an exponential probability distribution.

Create a probability distribution object with specified parameter values using makedist. Alternatively, fit a distribution to data using fitdist or the Distribution Fitting app.

## Construction

pd = makedist('Exponential') creates an exponential probability distribution object using the default parameter values.

pd = makedist('Exponential','mu',mu) creates an exponential probability distribution object using the specified parameter value.

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### mu — Mean1 (default) | positive scalar value

Mean of the exponential distribution, specified as a positive scalar value.

Data Types: single | double

## Properties

 mu Mean of the exponential distribution, stored as a positive scalar value. DistributionName Name of the probability distribution, stored as a valid probability distribution name string. This property is read-only. InputData Data used for distribution fitting, stored as a structure containing the following: data: Data vector used for distribution fitting.cens: Censoring vector, or empty if none.freq: Frequency vector, or empty if none. This property is read-only. IsTruncated Logical flag for truncated distribution, stored as a logical value. If IsTruncated equals 0, the distribution is not truncated. If IsTruncated equals 1, the distribution is truncated. This property is read-only. NumParameters Number of parameters for the probability distribution, stored as a positive integer value. This property is read-only. ParameterCovariance Covariance matrix of the parameter estimates, stored as a p-by-p matrix, where p is the number of parameters in the distribution. The (i,j) element is the covariance between the estimates of the ith parameter and the jth parameter. The (i,i) element is the estimated variance of the ith parameter. If parameter i is fixed rather than estimated by fitting the distribution to data, then the (i,i) elements of the covariance matrix are 0. This property is read-only. ParameterDescription Descriptions of distribution parameters, stored as a cell array of strings. Each cell contains a short description of one distribution parameter. This property is read-only. ParameterIsFixed Logical flag for fixed parameters, stored as an array of logical values. If 0, the corresponding parameter in the ParameterNames array is not fixed. If 1, the corresponding parameter in the ParameterNames array is fixed. This property is read-only. ParameterNames Names of distribution parameters, stored as a cell array of strings. This property is read-only. ParameterValues Values of distribution parameters, stored as a vector. This property is read-only. Truncation Truncation interval for the probability distribution, stored as a vector containing the lower and upper truncation boundaries. This property is read-only.

## Methods

### Inherited Methods

 cdf Cumulative distribution function of probability distribution object icdf Inverse cumulative distribution function of probability distribution object iqr Interquartile range of probability distribution object median Median of probability distribution object pdf Probability density function of probability distribution object random Generate random numbers from probability distribution object truncate Truncate probability distribution object
 mean Mean of probability distribution object negloglik Negative loglikelihood of probability distribution object paramci Confidence intervals for probability distribution parameters proflik Profile likelihood function for probability distribution object std Standard deviation of probability distribution object var Variance of probability distribution object

## Definitions

### Exponential Distribution

The exponential distribution is used to model events that occur randomly over time, and its main application area is studies of lifetimes. It is a special case of the gamma distribution with the shape parameter a = 1.

The exponential distribution uses the following parameters.

ParameterDescriptionSupport
muMean

The probability density function (pdf) is

## Examples

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### Create an Exponential Distribution Object Using Default Parameters

Create an exponential distribution object using the default parameter values.

`pd = makedist('Exponential')`
```pd =

ExponentialDistribution

Exponential distribution
mu = 1```

### Create an Exponential Distribution Object Using Specified Parameters

Create an exponential distribution object by specifying the parameter values.

`pd = makedist('Exponential','mu',2)`
```pd =

ExponentialDistribution

Exponential distribution
mu = 2```

Compute the variance of the distribution.

`v = var(pd)`
```v =

4```