# std

Class: prob.ToolboxFittableParametricDistribution
Package: prob

Standard deviation of probability distribution object

## Syntax

`s = std(pd)`

## Description

`s = std(pd)` returns the standard deviation `s` of the probability distribution `pd`.

## Input Arguments

collapse all

### `pd` — Probability distributionprobability distribution object

Probability distribution, specified as a probability distribution object. Create a probability distribution object with specified parameter values using `makedist`. Alternatively, create a probability distribution object by fitting it to data using `fitdist` or the Distribution Fitting app.

## Output Arguments

collapse all

### `s` — Standard deviationnonnegative scalar value

Standard deviation of the probability distribution, returned as a nonnegative scalar value.

## Examples

collapse all

### Standard Deviation of a Fitted Distribution

Load the sample data. Create a vector containing the first column of students' exam grade data.

```load examgrades; x = grades(:,1); ```

Fit a normal distribution object to the data.

`pd = fitdist(x,'Normal')`
```pd = NormalDistribution Normal distribution mu = 75.0083 [73.4321, 76.5846] sigma = 8.7202 [7.7391, 9.98843]```

Compute the standard deviation of the fitted distribution.

`s = std(pd)`
```s = 8.7202```

For a normal distribution, the standard deviation is equal to the parameter `sigma`.

### Standard Deviation of a Skewed Distribution

Create a Weibull probability distribution object

`pd = makedist('Weibull','a',5,'b',2)`
```pd = WeibullDistribution Weibull distribution A = 5 B = 2```

Compute the standard deviation of the distribution.

`s = std(pd)`
```s = 2.3163```