npm package: @stdlib/number-float64-base-identity
Description: Evaluate the identity function for a double-precision floating-point number.
Author: The Stdlib Authors
Latest version: 0.1.1

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</details>

# Identity Function

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

> Evaluate the [identity function][identity-function] of a double-precision floating-point number.

<section class="intro">

The [identity-function][identity-function] is defined as

<!-- <equation class="equation" label="eq:identity_function" align="center" raw="f(x) = x" alt="Identity function"> -->

<div class="equation" align="center" data-raw-text="f(x) = x" data-equation="eq:identity_function">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@ad7afa5d7ec1b1596f8a4828153d8c2e87a90161/lib/node_modules/@stdlib/number/float64/base/identity/docs/img/equation_identity_function.svg" alt="Identity function">
    <br>
</div>

<!-- </equation> -->

for all `x`.

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/number-float64-base-identity
```

</section>

<section class="usage">

## Usage

```javascript
var identity = require( '@stdlib/number-float64-base-identity' );
```

#### identity( x )

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

```javascript
var v = identity( -1.0 );
// returns -1.0

v = identity( 2.0 );
// returns 2.0

v = identity( 0.0 );
// returns 0.0

v = identity( -0.0 );
// returns -0.0

v = identity( NaN );
// returns NaN
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var identity = require( '@stdlib/number-float64-base-identity' );

var rand;
var i;

for ( i = 0; i < 100; i++ ) {
    rand = round( randu() * 100.0 ) - 50.0;
    console.log( 'identity(%d) = %d', rand, identity( rand ) );
}
```

</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/number/float64/base/identity.h"
```

#### stdlib_base_float64_identity( x )

Evaluates the identity function for a double-precision floating-point number.

```c
double y = stdlib_base_float64_identity( 2.0 );
// returns 2.0
```

The function accepts the following arguments:

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

```c
double stdlib_base_float64_identity( 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/number/float64/base/identity.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_float64_identity( x[ i ] );
        printf( "f(%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">

* * *

## See Also

-   <span class="package-name">[`@stdlib/number-float32/base/identity`][@stdlib/number/float32/base/identity]</span><span class="delimiter">: </span><span class="description">evaluate the identity function for a single-precision floating-point number.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<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/number-float64-base-identity/tree/deno
[deno-readme]: https://github.com/stdlib-js/number-float64-base-identity/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/number-float64-base-identity/tree/umd
[umd-readme]: https://github.com/stdlib-js/number-float64-base-identity/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/number-float64-base-identity/tree/esm
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/number-float64-base-identity/main/LICENSE

[identity-function]: https://en.wikipedia.org/wiki/Identity_function

<!-- <related-links> -->

[@stdlib/number/float32/base/identity]: https://www.npmjs.com/package/@stdlib/number-float32-base-identity

<!-- </related-links> -->

</section>

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