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# Unary

> Create a function which performs element-wise computation by applying a unary function to each element in an input ndarray.

<!-- 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">

The purpose of this package is to provide a thin wrapper around a lower-level interface supporting multiple dispatch based on the data types of provided ndarray arguments. The wrapper performs the following tasks:

-   validates input arguments.
-   casts input ndarrays according to a casting policy.
-   allocates an output ndarray according to an output data type policy.

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="usage">

## Usage

```javascript
var factory = require( '@stdlib/math/tools/unary' );
```

#### factory( fcn, idtypes, odtypes, policies )

Returns a function which performs element-wise computation by applying a unary function to each element in an input ndarray.

<!-- eslint-disable array-element-newline -->

```javascript
var base = require( '@stdlib/math/base/special/abs' );
var dispatch = require( '@stdlib/ndarray/dispatch' );
var unary = require( '@stdlib/ndarray/base/unary' );
var array = require( '@stdlib/ndarray/array' );

var types = [
    'float64', 'float64',
    'float64', 'generic',
    'generic', 'generic'
];
var data = [
    base,
    base,
    base
];
var dispatcher = dispatch( unary, types, data, 2, 1, 1 );

var idt = [ 'float64', 'generic' ];
var odt = idt;

var policies = {
    'output': 'real_and_generic',
    'casting': 'none'
};
var ufunc = factory( dispatcher, [ idt ], odt, policies );
```

The function has the following arguments:

-   **fcn**: function which applies a unary function to each element in an ndarray and assigns results to an output ndarray.

-   **idtypes**: list containing lists of supported input data types for each input ndarray argument.

-   **odtypes**: list of supported output data types.

-   **policies**: dispatch policies. Must have the following properties:

    -   **output**: output data type [policy][@stdlib/ndarray/output-dtype-policies].
    -   **casting**: input ndarray casting [policy][@stdlib/ndarray/input-casting-policies].

#### ufunc( x\[, options] )

Performs element-wise computation.

<!-- eslint-disable array-element-newline -->

```javascript
var base = require( '@stdlib/math/base/special/abs' );
var dispatch = require( '@stdlib/ndarray/dispatch' );
var unary = require( '@stdlib/ndarray/base/unary' );
var array = require( '@stdlib/ndarray/array' );

var types = [
    'float64', 'float64',
    'float64', 'generic',
    'generic', 'generic'
];
var data = [
    base,
    base,
    base
];
var dispatcher = dispatch( unary, types, data, 2, 1, 1 );

var idt = [ 'float64', 'generic' ];
var odt = idt;

var policies = {
    'output': 'real_and_generic',
    'casting': 'none'
};
var ufunc = factory( dispatcher, [ idt ], odt, policies );

var x = array( [ [ -1.0, -2.0 ], [ -3.0, -4.0 ] ] );
// returns <ndarray>

var y = ufunc( x );
// returns <ndarray>[ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ]
```

The function has the following parameters:

-   **x**: input ndarray.
-   **options**: function options (_optional_).

The function accepts the following options:

-   **dtype**: output ndarray data type. Setting this option, overrides the output data type policy.
-   **order**: output ndarray order.

By default, the function returns an ndarray having a data type determined by the output data type policy. To override the default behavior, set the `dtype` option.

<!-- eslint-disable array-element-newline -->

```javascript
var base = require( '@stdlib/math/base/special/abs' );
var dispatch = require( '@stdlib/ndarray/dispatch' );
var unary = require( '@stdlib/ndarray/base/unary' );
var getDType = require( '@stdlib/ndarray/dtype' );
var array = require( '@stdlib/ndarray/array' );

var types = [
    'float64', 'float64',
    'float64', 'generic',
    'generic', 'generic'
];
var data = [
    base,
    base,
    base
];
var dispatcher = dispatch( unary, types, data, 2, 1, 1 );

var idt = [ 'float64', 'generic' ];
var odt = idt;

var policies = {
    'output': 'real_and_generic',
    'casting': 'none'
};
var ufunc = factory( dispatcher, [ idt ], odt, policies );

var x = array( [ [ -1.0, -2.0 ], [ -3.0, -4.0 ] ] );
// returns <ndarray>

var y = ufunc( x, {
    'dtype': 'generic'
});
// returns <ndarray>

var dt = getDType( y );
// returns 'generic'
```

#### ufunc.assign( x, out )

Performs element-wise computation and assigns results to a provided output ndarray.

<!-- eslint-disable array-element-newline -->

```javascript
var base = require( '@stdlib/math/base/special/abs' );
var dispatch = require( '@stdlib/ndarray/dispatch' );
var unary = require( '@stdlib/ndarray/base/unary' );
var zerosLike = require( '@stdlib/ndarray/zeros-like' );
var array = require( '@stdlib/ndarray/array' );

var types = [
    'float64', 'float64',
    'float64', 'generic',
    'generic', 'generic'
];
var data = [
    base,
    base,
    base
];
var dispatcher = dispatch( unary, types, data, 2, 1, 1 );

var idt = [ 'float64', 'generic' ];
var odt = idt;

var policies = {
    'output': 'real_and_generic',
    'casting': 'none'
};
var ufunc = factory( dispatcher, [ idt ], odt, policies );

var x = array( [ [ -1.0, -2.0 ], [ -3.0, -4.0 ] ] );
// returns <ndarray>

var y = zerosLike( x );
// returns <ndarray>

var out = ufunc.assign( x, y );
// returns <ndarray>[ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ]

var bool = ( out === y );
// returns true
```

The method has the following parameters:

-   **x**: input ndarray.
-   **out**: output ndarray.

</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">

## Notes

-   A provided unary function should have the following signature:

    ```text
    f( x, y )
    ```

    where

    -   **x**: input ndarray.
    -   **y**: output ndarray.

-   The output data type policy only applies to the function returned by the main function. For the `assign` method, the output ndarray is allowed to have any supported output data type.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint-disable array-element-newline -->

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

```javascript
var base = require( '@stdlib/math/base/special/abs' );
var basef = require( '@stdlib/math/base/special/absf' );
var uniform = require( '@stdlib/random/uniform' );
var dispatch = require( '@stdlib/ndarray/dispatch' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var unary = require( '@stdlib/ndarray/base/unary' );
var ufunc = require( '@stdlib/math/tools/unary' );

// Create a function which dispatches based on argument data types:
var types = [
    'float64', 'float64',
    'float32', 'float32',
    'generic', 'generic'
];
var data = [
    base,
    basef,
    base
];
var dispatcher = dispatch( unary, types, data, 2, 1, 1 );

// Define the supported input and output data types:
var idt = [ 'float64', 'float32', 'generic' ];
var odt = [ 'float64', 'float32', 'generic' ];

// Define dispatch policies:
var policies = {
    'output': 'same',
    'casting': 'none'
};

// Create a function that performs element-wise computation:
var abs = ufunc( dispatcher, [ idt ], odt, policies );

// Generate an array of random numbers:
var x = uniform( [ 5, 5 ], -10.0, 10.0, {
    'dtype': 'float64'
});
console.log( ndarray2array( x ) );

// Perform element-wise computation:
var y = abs( x );
console.log( ndarray2array( y ) );
```

</section>

<!-- /.examples -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- 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">

[@stdlib/ndarray/output-dtype-policies]: https://www.npmjs.com/package/@stdlib/ndarray-output-dtype-policies

[@stdlib/ndarray/input-casting-policies]: https://www.npmjs.com/package/@stdlib/ndarray-input-casting-policies

</section>

<!-- /.links -->
