@stdlib/random-strided-chisquare/README.md

Fill a strided array with pseudorandom numbers drawn from a chi-square distribution.

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# Chi-square Random Numbers

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> Fill a strided array with pseudorandom numbers drawn from a [chi-square][@stdlib/random/base/chisquare] distribution.

<section class="installation">

## Installation

```bash
npm install @stdlib/random-strided-chisquare
```

</section>

<section class="usage">

## Usage

```javascript
var chisquare = require( '@stdlib/random-strided-chisquare' );
```

#### chisquare( N, k, sk, out, so )

Fills a strided array with pseudorandom numbers drawn from a [chi-square][@stdlib/random/base/chisquare] distribution.

```javascript
var Float64Array = require( '@stdlib/array-float64' );

// Create an array:
var out = new Float64Array( 10 );

// Fill the array with pseudorandom numbers:
chisquare( out.length, [ 2.0 ], 0, out, 1 );
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **k**: rate parameter.
-   **sk**: index increment for `k`.
-   **out**: output array.
-   **so**: index increment for `out`.

The `N` and stride parameters determine which strided array elements are accessed at runtime. For example, to access every other value in `out`,

```javascript
var out = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

chisquare( 3, [ 2.0 ], 0, out, 2 );
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

<!-- eslint-disable stdlib/capitalized-comments -->

```javascript
var Float64Array = require( '@stdlib/array-float64' );

// Initial array:
var k0 = new Float64Array( [ 2.0, 2.0, 2.0, 2.0, 2.0, 2.0 ] );

// Create offset view:
var k1 = new Float64Array( k0.buffer, k0.BYTES_PER_ELEMENT*3 ); // start at 4th element

// Create an output array:
var out = new Float64Array( 3 );

// Fill the output array:
chisquare( out.length, k1, -1, out, 1 );
```

#### chisquare.ndarray( N, k, sk, ok, out, so, oo )

Fills a strided array with pseudorandom numbers drawn from a [chi-square][@stdlib/random/base/chisquare] distribution using alternative indexing semantics.

```javascript
var Float64Array = require( '@stdlib/array-float64' );

// Create an array:
var out = new Float64Array( 10 );

// Fill the array with pseudorandom numbers:
chisquare.ndarray( out.length, [ 2.0 ], 0, 0, out, 1, 0 );
```

The function has the following additional parameters:

-   **ok**: starting index for `k`.
-   **oo**: starting index for `out`.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the offset parameters support indexing semantics based on starting indices. For example, to access every other value in `out` starting from the second value,

```javascript
var out = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

chisquare.ndarray( 3, [ 2.0 ], 0, 0, out, 2, 1 );
```

#### chisquare.factory( \[options] )

Returns a function for filling strided arrays with pseudorandom numbers drawn from a [chi-square][@stdlib/random/base/chisquare] distribution.

```javascript
var Float64Array = require( '@stdlib/array-float64' );

var random = chisquare.factory();
// returns <Function>

// Create an array:
var out = new Float64Array( 10 );

// Fill the array with pseudorandom numbers:
random( out.length, [ 2.0 ], 0, out, 1 );
```

The function accepts the following `options`:

-   **prng**: pseudorandom number generator for generating uniformly distributed pseudorandom numbers on the interval `[0,1)`. If provided, the function **ignores** both the `state` and `seed` options. In order to seed the underlying pseudorandom number generator, one must seed the provided `prng` (assuming the provided `prng` is seedable).
-   **seed**: pseudorandom number generator seed.
-   **state**: a [`Uint32Array`][@stdlib/array/uint32] containing pseudorandom number generator state. If provided, the function ignores the `seed` option.
-   **copy**: `boolean` indicating whether to copy a provided pseudorandom number generator state. Setting this option to `false` allows sharing state between two or more pseudorandom number generators. Setting this option to `true` ensures that an underlying generator has exclusive control over its internal state. Default: `true`.

To use a custom PRNG as the underlying source of uniformly distributed pseudorandom numbers, set the `prng` option.

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var minstd = require( '@stdlib/random-base-minstd' );

var opts = {
    'prng': minstd.normalized
};
var random = chisquare.factory( opts );

var out = new Float64Array( 10 );
random( out.length, [ 2.0 ], 0, out, 1 );
```

To seed the underlying pseudorandom number generator, set the `seed` option.

```javascript
var Float64Array = require( '@stdlib/array-float64' );

var opts = {
    'seed': 12345
};
var random = chisquare.factory( opts );

var out = new Float64Array( 10 );
random( out.length, [ 2.0 ], 0, out, 1 );
```

* * *

#### random.PRNG

The underlying pseudorandom number generator.

```javascript
var prng = chisquare.PRNG;
// returns <Function>
```

#### chisquare.seed

The value used to seed the underlying pseudorandom number generator.

```javascript
var seed = chisquare.seed;
// returns <Uint32Array>
```

If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`.

```javascript
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;

var random = chisquare.factory({
    'prng': minstd
});
// returns <Function>

var seed = random.seed;
// returns null
```

#### chisquare.seedLength

Length of underlying pseudorandom number generator seed.

```javascript
var len = chisquare.seedLength;
// returns <number>
```

If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`.

```javascript
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;

var random = chisquare.factory({
    'prng': minstd
});
// returns <Function>

var len = random.seedLength;
// returns null
```

#### chisquare.state

Writable property for getting and setting the underlying pseudorandom number generator state.

```javascript
var state = chisquare.state;
// returns <Uint32Array>
```

If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`.

```javascript
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;

var random = chisquare.factory({
    'prng': minstd
});
// returns <Function>

var state = random.state;
// returns null
```

#### chisquare.stateLength

Length of underlying pseudorandom number generator state.

```javascript
var len = chisquare.stateLength;
// returns <number>
```

If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`.

```javascript
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;

var random = chisquare.factory({
    'prng': minstd
});
// returns <Function>

var len = random.stateLength;
// returns null
```

#### chisquare.byteLength

Size (in bytes) of underlying pseudorandom number generator state.

```javascript
var sz = chisquare.byteLength;
// returns <number>
```

If the `factory` method is provided a PRNG for uniformly distributed numbers, the associated property value on the returned function is `null`.

```javascript
var minstd = require( '@stdlib/random-base-minstd-shuffle' ).normalized;

var random = chisquare.factory({
    'prng': minstd
});
// returns <Function>

var sz = random.byteLength;
// returns null
```

</section>

<!-- /.usage -->

<section class="notes">

* * *

## Notes

-   If `N <= 0`, both `chisquare` and `chisquare.ndarray` leave the output array unchanged.
-   Both `chisquare` and `chisquare.ndarray` support array-like objects having getter and setter accessors for array element access.

</section>

<!-- /.notes -->

<section class="examples">

* * *

## Examples

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

```javascript
var zeros = require( '@stdlib/array-zeros' );
var zeroTo = require( '@stdlib/array-zero-to' );
var logEach = require( '@stdlib/console-log-each' );
var chisquare = require( '@stdlib/random-strided-chisquare' );

// Specify a PRNG seed:
var opts = {
    'seed': 1234
};

// Create a seeded PRNG:
var rand1 = chisquare.factory( opts );

// Create an array:
var x1 = zeros( 10, 'float64' );

// Fill the array with pseudorandom numbers:
rand1( x1.length, [ 2.0 ], 0, x1, 1 );

// Create another function for filling strided arrays:
var rand2 = chisquare.factory( opts );
// returns <Function>

// Create a second array:
var x2 = zeros( 10, 'generic' );

// Fill the array with the same pseudorandom numbers:
rand2( x2.length, [ 2.0 ], 0, x2, 1 );

// Create a list of indices:
var idx = zeroTo( x1.length, 'generic' );

// Print the array contents:
logEach( 'x1[%d] = %.2f; x2[%d] = %.2f', idx, x1, idx, x2 );
```

</section>

<!-- /.examples -->

<!-- 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/random-base/chisquare`][@stdlib/random/base/chisquare]</span><span class="delimiter">: </span><span class="description">Chi-square distributed pseudorandom numbers.</span>
-   <span class="package-name">[`@stdlib/random-array/chisquare`][@stdlib/random/array/chisquare]</span><span class="delimiter">: </span><span class="description">create an array containing pseudorandom numbers drawn from a chi-square distribution.</span>

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

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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].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

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