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# cphase

> Compute the [argument][complex-number-argument] of a double-precision complex floating-point number in radians.

<section class="intro">

The [argument][complex-number-argument] of a complex number, also known as the **phase**, is the angle of the radius extending from the origin to the complex number plotted in the complex plane and the positive real axis.

</section>

<!-- /.intro -->

<section class="usage">

## Usage

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

#### cphase( z )

Computes the [argument][complex-number-argument] of a double-precision complex floating-point number.

```javascript
var Complex128 = require( '@stdlib/complex/float64/ctor' );

var phi = cphase( new Complex128( 5.0, 3.0 ) );
// returns ~0.5404
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

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

```javascript
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var uniform = require( '@stdlib/random/base/uniform' );
var cphase = require( '@stdlib/math/base/special/cphase' );

var z;
var i;

for ( i = 0; i < 100; i++ ) {
    z = new Complex128( uniform( -500.0, 500.0 ), uniform( -500.0, 500.0 ) );
    console.log( 'arg(%s) = %d', z.toString(), cphase( z ) );
}
```

</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/cphase.h"
```

#### stdlib_base_cphase( z )

Computes the [argument][complex-number-argument] of a double-precision complex floating-point number.

```c
#include "stdlib/complex/float64/ctor.h"
#include "stdlib/complex/float64/real.h"
#include "stdlib/complex/float64/imag.h"

stdlib_complex128_t z = stdlib_complex128( 5.0, 3.0 );
double out = stdlib_base_cphase( z );
// returns ~0.5404
```

The function accepts the following arguments:

-   **z**: `[in] stdlib_complex128_t` input value.

```c
double stdlib_base_cphase( const stdlib_complex128_t z );
```

</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/cphase.h"
#include "stdlib/complex/float64/ctor.h"
#include "stdlib/complex/float64/reim.h"
#include <stdio.h>

int main( void ) {
    const stdlib_complex128_t x[] = {
        stdlib_complex128( 3.14, 1.5 ),
        stdlib_complex128( -3.14, -1.5 ),
        stdlib_complex128( 0.0, 0.0 ),
        stdlib_complex128( 0.0/0.0, 0.0/0.0 )
    };

    stdlib_complex128_t v;
    double re;
    double im;
    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        v = x[ i ];
        y = stdlib_base_cphase( v );
        stdlib_complex128_reim( v, &re, &im );
        printf( "cphase(%lf + %lfi) = %lf\n", re, im, 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/math/base/special/cabs`][@stdlib/math/base/special/cabs]</span><span class="delimiter">: </span><span class="description">compute the absolute value of a double-precision complex 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="links">

[complex-number-argument]: https://en.wikipedia.org/wiki/Argument_%28complex_analysis%29

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

[@stdlib/math/base/special/cabs]: https://github.com/stdlib-js/math/tree/main/base/special/cabs

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

</section>

<!-- /.links -->
