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# aversinf

> Compute the [inverse versed sine][inverse-versed-sine] of a single-precision floating-point number (in radians).

<section class="intro">

The [inverse versed sine][inverse-versed-sine] is defined as

<!-- <equation class="equation" label="eq:arcversine" align="center" raw="\operatorname{aversinf}(\theta) = \arccos(1-\theta)" alt="Inverse versed sine."> -->

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="usage">

## Usage

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

#### aversinf( x )

Computes the [inverse versed sine][inverse-versed-sine] of a single-precision floating-point number (in radians).

```javascript
var v = aversinf( 0.0 );
// returns 0.0

v = aversinf( 3.141592653589793 / 2.0 );
// returns ~2.1783

v = aversinf( 3.141592653589793 / 6.0 );
// returns ~1.0742
```

If `x < 0`, `x > 2`, or `x` is `NaN`, the function returns `NaN`.

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

v = aversinf( 3.14 );
// returns NaN

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

</section>

<!-- /.usage -->

<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 aversinf = require( '@stdlib/math/base/special/aversinf' );

var x = uniform( 100, 0.0, 2.0, {
    'dtype': 'float32'
});

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

</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/aversinf.h"
```

#### stdlib_base_aversinf( x )

Computes the [inverse versed sine][inverse-versed-sine] of a single-precision floating-point number (in radians).

```c
float out = stdlib_base_aversinf( 3.141592653589793f / 2.0f );
// returns ~2.1783f
```

If `x < 0`, `x > 2`, or `x` is `NaN`, the function returns `NaN`.

```c
float out = stdlib_base_aversinf( 3.141592653589793f );
// returns NaN
```

The function accepts the following arguments:

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

```c
float stdlib_base_aversinf( const float 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/aversinf.h"
#include <stdio.h>

int main( void ) {
    const float x[] = { -2.5f, -2.0f, -1.5f, -1.0f, -0.5f, 0.5f, 1.0f, 1.5f, 2.0f, 2.5f };

    float v;
    int i;
    for ( i = 0; i < 10; i++ ) {
        v = stdlib_base_aversinf( x[ i ] );
        printf( "aversinf(%f) = %f\n", x[ i ], v );
    }
}
```

</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 -->

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

<section class="links">

[inverse-versed-sine]: https://en.wikipedia.org/wiki/Versine

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

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

</section>

<!-- /.links -->
