npm package: @stdlib/stats-base-dists-halfnormal-kurtosis
Description: Half-normal distribution excess kurtosis.
Author: The Stdlib Authors
Latest version: 0.1.1

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# Kurtosis

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> [Half-normal][half-normal-distribution] distribution [excess kurtosis][kurtosis].

<section class="intro">

The [excess kurtosis][kurtosis] of a [half-normal][half-normal-distribution] distribution with scale `sigma > 0` is

<!-- <equation class="equation" label="eq:halfnormal_kurtosis" align="center" raw="\gamma_2 = \frac{8(\pi-3)}{(\pi-2)^2}" alt="Excess kurtosis for a half-normal distribution."> -->

<div class="equation" align="center" data-raw-text="\gamma_2 = \frac{8(\pi-3)}{(\pi-2)^2}" data-equation="eq:halfnormal_kurtosis">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@2d398018e6a1275033c4ad59453a233302c3409d/lib/node_modules/@stdlib/stats/base/dists/halfnormal/kurtosis/docs/img/equation_halfnormal_kurtosis.svg" alt="Excess kurtosis for a half-normal distribution.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/stats-base-dists-halfnormal-kurtosis
```

</section>

<section class="usage">

## Usage

```javascript
var kurtosis = require( '@stdlib/stats-base-dists-halfnormal-kurtosis' );
```

#### kurtosis( sigma )

Returns the [excess kurtosis][kurtosis] of a [half-normal][half-normal-distribution] distribution with scale parameter `sigma`.

```javascript
var x = kurtosis( 1.0 );
// returns ~0.869

var y = kurtosis( 4.0 );
// returns ~0.869
```

If provided `sigma <= 0`, the function returns `NaN`.

```javascript
var x = kurtosis( 0.0 );
// returns NaN

var y = kurtosis( -1.0 );
// returns NaN
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var uniform = require( '@stdlib/random-array-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var kurtosis = require( '@stdlib/stats-base-dists-halfnormal-kurtosis' );

var opts = {
    'dtype': 'float64'
};
var sigma = uniform( 10, 0.0, 20.0, opts );

logEachMap( 'σ: %0.4f, Kurt(X;σ): %0.4f', sigma, kurtosis );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/stats/base/dists/halfnormal/kurtosis.h"
```

#### stdlib_base_dists_halfnormal_kurtosis( sigma )

Returns the [excess kurtosis][kurtosis] of a [half-normal][half-normal-distribution] distribution with scale parameter `sigma`.

```c
double out = stdlib_base_dists_halfnormal_kurtosis( 1.0 );
// returns ~0.869
```

The function accepts the following arguments:

-   **sigma**: `[in] double` scale parameter.

```c
double stdlib_base_dists_halfnormal_kurtosis( const double sigma );
```

</section>

<!-- /.usage -->

<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

<!-- /.notes -->

<!-- C API usage examples. -->

<section class="examples">

### Examples

```c
#include "stdlib/stats/base/dists/halfnormal/kurtosis.h"
#include <stdlib.h>
#include <stdio.h>

static double random_uniform( const double min, const double max ) {
    double v = (double)rand() / ( (double)RAND_MAX + 1.0 );
    return min + ( v*(max-min) );
}

int main( void ) {
    double sigma;
    double y;
    int i;

    for ( i = 0; i < 10; i++ ) {
        sigma = random_uniform( 0.0, 20.0 );
        y = stdlib_base_dists_halfnormal_kurtosis( sigma );
        printf( "σ: %lf, Kurt(σ): %lf\n", sigma, y );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/stats-base-dists-halfnormal-kurtosis/main/LICENSE

[half-normal-distribution]: https://en.wikipedia.org/wiki/Half-normal_distribution

[kurtosis]: https://en.wikipedia.org/wiki/Kurtosis

</section>

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