# @stdlib/math-base-special-rsqrt 0.1.1 • Public • Published

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# Reciprocal Square Root

Compute the reciprocal of the principal square root of a double-precision floating-point number.

The reciprocal of the principal square root is defined as

## Installation

`npm install @stdlib/math-base-special-rsqrt`

## Usage

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

#### rsqrt( x )

Computes the reciprocal (inverse) square root of a double-precision floating-point number.

```var v = rsqrt( 1.0 );
// returns 1.0

v = rsqrt( 4.0 );
// returns 0.5

v = rsqrt( 100.0 );
// returns 0.1

v = rsqrt( 0.0 );
// returns Infinity

v = rsqrt( NaN );
// returns NaN

v = rsqrt( Infinity );
// returns 0.0```

For negative numbers, the reciprocal square root is not defined.

```var v = rsqrt( -4.0 );
// returns NaN```

## Examples

```var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var rsqrt = require( '@stdlib/math-base-special-rsqrt' );

var x;
var i;

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

## C APIs

### Usage

`#include "stdlib/math/base/special/rsqrt.h"`

#### stdlib_base_rsqrt( x )

Computes the reciprocal (inverse) square root of a double-precision floating-point number.

```double y = stdlib_base_rsqrt( 4.0 );
// returns 0.5```

The function accepts the following arguments:

• x: `[in] double` input value.
`double stdlib_base_rsqrt( const double x );`

### Examples

```#include "stdlib/math/base/special/rsqrt.h"
#include <stdio.h>

int main( void ) {
const double x[] = { 3.14, 9.0, 0.0, 0.0/0.0 };

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

## Notice

This package is part of 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, see the main project repository.

#### Community ## Package Sidebar

### Install

`npm i @stdlib/math-base-special-rsqrt`

### Repository

github.com/stdlib-js/math-base-special-rsqrt

stdlib.io

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