npm package: @stdlib/math-base-special-signum
Description: Evaluate the signum function for a double-precision floating-point number.
Author: The Stdlib Authors
Latest version: 0.2.3

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# Signum

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

> [Signum][signum] function.

<section class="intro">

The [signum][signum] function is defined as

<!-- <equation class="equation" label="eq:signum_function" align="center" raw="\operatorname{sign}(x) := \begin{cases} -1 & \textrm{if}\ x < 0 \\ 0 & \textrm{if}\ x = 0 \\ 1 & \textrm{if}\ x > 0 \end{cases}" alt="Signum function"> -->

<div class="equation" align="center" data-raw-text="\operatorname{sign}(x) := \begin{cases} -1 &amp; \textrm{if}\ x &lt; 0 \\ 0 &amp; \textrm{if}\ x = 0 \\ 1 &amp; \textrm{if}\ x &gt; 0 \end{cases}" data-equation="eq:signum_function">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/signum/docs/img/equation_signum_function.svg" alt="Signum function">
    <br>
</div>

<!-- </equation> -->

for any real number `x`.

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/math-base-special-signum
```

</section>

<section class="usage">

## Usage

```javascript
var signum = require( '@stdlib/math-base-special-signum' );
```

#### signum( x )

Evaluates the [signum][signum] function for a double-precision floating-point number.

```javascript
var sign = signum( -5.0 );
// returns -1

sign = signum( 5.0 );
// returns 1

sign = signum( -0.0 );
// returns -0

sign = signum( 0.0 );
// returns 0

sign = signum( NaN );
// returns NaN
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

Table of results:

| Value   | Sign  |
| ------- | ----- |
| `x > 0` | `+1`  |
| `x < 0` | `-1`  |
| `0`     | `0`   |
| `-0`    | `-0`  |
| `NaN`   | `NaN` |

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var signum = require( '@stdlib/math-base-special-signum' );

var opts = {
    'dtype': 'float64'
};
var x = discreteUniform( 100, -50, 50, opts );

logEachMap( 'signum(%d) = %0.4f', x, signum );
```

</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/math/base/special/signum.h"
```

#### stdlib_base_signum( x )

Evaluates the [signum][signum] function for a double-precision floating-point number.

```c
double y = stdlib_base_signum( -9.0 );
// returns -1.0
```

The function accepts the following arguments:

-   **x**: `[in] double` input value.

```c
double stdlib_base_signum( const double x );
```

</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/math/base/special/signum.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { 3.14, -3.14, 0.0, 0.0/0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_signum( x[ i ] );
        printf( "signum(%lf) = %lf\n", x[ i ], 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

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

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

</section>

<!-- /.stdlib -->

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[stdlib]: https://github.com/stdlib-js/stdlib

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/math-base-special-signum/tree/deno
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/math-base-special-signum/main/LICENSE

[signum]: https://en.wikipedia.org/wiki/Sign_function

</section>

<!-- /.links -->