npm package: @stdlib/math-base-special-csignum
Description: Evaluate the signum function of a double-precision complex floating-point number.
Author: The Stdlib Authors
Latest version: 0.2.3

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# csignum

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

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/math-base-special-csignum
```

</section>

<section class="usage">

## Usage

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

#### csignum( z )

Evaluates the [signum][signum] function of a double-precision complex floating-point number.

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

var v = csignum( new Complex128( -4.2, 5.5 ) );
// returns <Complex128>[ -0.6069136033622302, 0.79476781392673 ]

v = csignum( new Complex128( 0.0, 0.0 ) );
// returns <Complex128>[ 0.0, 0.0 ]

v = csignum( new Complex128( NaN, NaN ) );
// returns <Complex128>[ NaN, NaN ]
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

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

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

var rand = uniform( -50.0, 50.0 );

var z;
var i;
for ( i = 0; i < 100; i++ ) {
    z = new Complex128( rand(), rand() );
    console.log( 'csignum(%s) = %s', z, csignum( z ) );
}
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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</section>

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<section class="usage">

### Usage

```c
#include "stdlib/math/base/special/csignum.h"
```

#### stdlib_base_csignum( z )

Evaluates the [signum][signum] function 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( -4.2, 5.5 );

stdlib_complex128_t out = stdlib_base_csignum( z );

double re = stdlib_complex128_real( out );
// returns -0.6069136033622302

double im = stdlib_complex128_imag( out );
// returns 0.79476781392673
```

The function accepts the following arguments:

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

```c
stdlib_complex128_t stdlib_base_csignum( 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/csignum.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;
    stdlib_complex128_t y;
    double re1;
    double im1;
    double re2;
    double im2;
    int i;
    for ( i = 0; i < 4; i++ ) {
        v = x[ i ];
        y = stdlib_base_csignum( v );
        stdlib_complex128_reim( v, &re1, &im1 );
        stdlib_complex128_reim( y, &re2, &im2 );
        printf( "csignum(%lf + %lfi) = %lf + %lfi\n", re1, im1, re2, im2 );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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</section>

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* * *

## See Also

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

</section>

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* * *

## 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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[signum]: https://en.wikipedia.org/wiki/Sign_function

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