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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.

Input Arguments

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

Data Types: `single` | `double`

Properties

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

Data Types: `single` | `double`

Probability distribution name, stored as a character vector. This property is read-only.

Data Types: `char`

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.

Data Types: `struct`

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.

Data Types: `logical`

Number of parameters for the probability distribution, stored as a positive integer value. This property is read-only.

Data Types: `single` | `double`

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 `i`th parameter and the `j`th parameter. The (`i`,`i`) element is the estimated variance of the `i`th 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.

Data Types: `single` | `double`

Distribution parameter descriptions, stored as a cell array of character vectors. Each cell contains a short description of one distribution parameter. This property is read-only.

Data Types: `char`

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.

Data Types: `logical`

Distribution parameter names, stored as a cell array of character vectors. This property is read-only.

Data Types: `char`

Distribution parameter values, stored as a vector. This property is read-only.

Data Types: `single` | `double`

Truncation interval for the probability distribution, stored as a vector containing the lower and upper truncation boundaries. This property is read-only.

Data Types: `single` | `double`

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 log likelihood 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
`mu`Mean$\mu >0$

The probability density function (pdf) is

`$f\left(x|\mu \right)=\frac{1}{\mu }{e}^{\frac{-x}{\mu }}\text{ };\text{ }x\ge 0\text{\hspace{0.17em}}.$`

Examples

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Create an exponential distribution object using the default parameter values.

`pd = makedist('Exponential')`
```pd = ExponentialDistribution Exponential distribution mu = 1```

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```