npm package: @stdlib/stats-base-dists-f-entropy
Description: F distribution differential entropy.
Author: The Stdlib Authors
Latest version: 0.3.1

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# Entropy

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

> [F][f-distribution] distribution [differential entropy][entropy].

<!-- 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">

The [differential entropy][entropy] (in [nats][nats]) for a [F][f-distribution] random variable is

<!-- <equation class="equation" label="eq:f_entropy" align="center" raw="h\left( X \right) = \ln\left( \tfrac{d_2}{d_1} \Gamma\left( \tfrac{d_1}{2} \right) \Gamma\left( \tfrac{d_2}{2} \right) \Gamma\left( \tfrac{d_1+d_2}{2} \right) \right) \\ + \left( 1-\tfrac{d_1}{2} \right) \Psi\left( \tfrac{d_1}{2} \right) +  \left( 1-\tfrac{d_2}{2} \right) \Psi\left( \tfrac{d_2}{2} \right) + \tfrac{d_1+d_2}{2} \Psi\left( \tfrac{d_1+d_2}{2} \right)" alt="Differential entropy for an F distribution."> -->

<div class="equation" align="center" data-raw-text="h\left( X \right) = \ln\left( \tfrac{d_2}{d_1} \Gamma\left( \tfrac{d_1}{2} \right) \Gamma\left( \tfrac{d_2}{2} \right) \Gamma\left( \tfrac{d_1+d_2}{2} \right) \right) \\ + \left( 1-\tfrac{d_1}{2} \right) \Psi\left( \tfrac{d_1}{2} \right) +  \left( 1-\tfrac{d_2}{2} \right) \Psi\left( \tfrac{d_2}{2} \right) + \tfrac{d_1+d_2}{2} \Psi\left( \tfrac{d_1+d_2}{2} \right)" data-equation="eq:f_entropy">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@591cf9d5c3a0cd3c1ceec961e5c49d73a68374cb/lib/node_modules/@stdlib/stats/base/dists/f/entropy/docs/img/equation_f_entropy.svg" alt="Differential entropy for an F distribution.">
    <br>
</div>

<!-- </equation> -->

where `d1` is the numerator degrees of freedom, `d2` is the denominator degrees of freedom, and `Γ` and `Ψ` denote the [gamma][gamma-function] and [digamma][digamma] functions, respectively.

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/stats-base-dists-f-entropy
```

</section>

<section class="usage">

## Usage

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

#### entropy( d1, d2 )

Returns the [differential entropy][entropy] of an [F][f-distribution] distribution with numerator degrees of freedom `d1` and denominator degrees of freedom `d2` (in [nats][nats]).

```javascript
var v = entropy( 4.0, 7.0 );
// returns ~1.277

v = entropy( 4.0, 12.0 );
// returns ~1.12

v = entropy( 8.0, 2.0 );
// returns ~2.144
```

If provided `NaN` as any argument, the function returns `NaN`.

```javascript
var v = entropy( NaN, 7.0 );
// returns NaN

v = entropy( 3.0, NaN );
// returns NaN
```

If provided `d1 <= 0`, the function returns `NaN`.

```javascript
var v = entropy( 0.0, 2.0 );
// returns NaN

v = entropy( -1.0, 1.0 );
// returns NaN
```

If provided `d2 <= 0`, the function returns `NaN`.

```javascript
var v = entropy( 3.0, 0.0 );
// returns NaN

v = entropy( 3.0, -1.0 );
// returns NaN
```

</section>

<!-- /.usage -->

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

<section class="notes">

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<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 EPS = require( '@stdlib/constants-float64-eps' );
var entropy = require( '@stdlib/stats-base-dists-f-entropy' );

var opts = {
    'dtype': 'float64'
};
var d1 = uniform( 10, EPS, 10.0, opts );
var d2 = uniform( 10, EPS, 20.0, opts );

logEachMap( 'd1: %0.4f, d2: %0.4f, h(X;d1,d2): %0.4f', d1, d2, entropy );
```

</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/f/entropy.h"
```

#### stdlib_base_dists_f_entropy( d1, d2 )

Evaluates the [differential entropy][entropy] of an [F][f-distribution] distribution with numerator degrees of freedom `d1` and denominator degrees of freedom `d2` (in [nats][nats]).

```c
double out = stdlib_base_dists_f_entropy( 3.0, 7.0 );
// returns ~1.298
```

The function accepts the following arguments:

-   **d1**: `[in] double` numerator degrees of freedom.
-   **d2**: `[in] double` denominator degrees of freedom.

```c
double stdlib_base_dists_f_entropy( const double d1, const double d2 );
```

</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/f/entropy.h"
#include "stdlib/constants/float64/eps.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 d1;
    double d2;
    double y;
    int i;

    for ( i = 0; i < 25; i++ ) {
        d1 = random_uniform( STDLIB_CONSTANT_FLOAT64_EPS, 10.0 );
        d2 = random_uniform( STDLIB_CONSTANT_FLOAT64_EPS, 10.0 );
        y = stdlib_base_dists_f_entropy( d1, d2 );
        printf( "d1: %lf, d2: %lf, h(X;d1,d2): %lf\n", d1, d2, y );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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<section class="references">

</section>

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<section class="related">

</section>

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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].

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[f-distribution]: https://en.wikipedia.org/wiki/F_distribution

[entropy]: https://en.wikipedia.org/wiki/Entropy_%28information_theory%29

[nats]: https://en.wikipedia.org/wiki/Nat_%28unit%29

[gamma-function]: https://en.wikipedia.org/wiki/Gamma_function

[digamma]: https://en.wikipedia.org/wiki/Digamma_function

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