# Square Root
> Compute the principal [square root][square-root] of a double-precision floating-point number.
The principal [square root][square-root] is defined as
## Usage
```javascript
var sqrt = require( '@stdlib/math/base/special/sqrt' );
```
#### sqrt( x )
Computes the principal [square root][square-root] of a double-precision floating-point number.
```javascript
var v = sqrt( 4.0 );
// returns 2.0
v = sqrt( 9.0 );
// returns 3.0
v = sqrt( 0.0 );
// returns 0.0
v = sqrt( NaN );
// returns NaN
```
For negative numbers, the principal [square root][square-root] is **not** defined.
```javascript
var v = sqrt( -4.0 );
// returns NaN
```
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var sqrt = require( '@stdlib/math/base/special/sqrt' );
var x;
var i;
for ( i = 0; i < 100; i++ ) {
x = round( randu() * 100.0 );
console.log( 'sqrt(%d) = %d', x, sqrt( x ) );
}
```
* * *
## C APIs
### Usage
```c
#include "stdlib/math/base/special/sqrt.h"
```
#### stdlib_base_sqrt( x )
Computes the principal [square root][square-root] of a double-precision floating-point number.
```c
double y = stdlib_base_sqrt( 9.0 );
// returns 3.0
```
The function accepts the following arguments:
- **x**: `[in] double` input value.
```c
double stdlib_base_sqrt( const double x );
```
### Examples
```c
#include "stdlib/math/base/special/sqrt.h"
#include
int main() {
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_sqrt( x[ i ] );
printf( "sqrt(%lf) = %lf\n", x[ i ], y );
}
}
```
[square-root]: https://en.wikipedia.org/wiki/Square_root
