time-to-botec/js/node_modules/@stdlib/random/base/randn/README.md

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# randn

> Standard normally distributed pseudorandom numbers.

<section class="usage">

## Usage

```javascript
var randn = require( '@stdlib/random/base/randn' );
```

#### randn()

Returns a standard normally distributed pseudorandom number.

```javascript
var r = randn();
// returns <number>
```

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

Returns a pseudorandom number generator for creating standard normally distributed random numbers.

```javascript
var rand = randn.factory();
```

The function accepts the following `options`:

-   **name**: name of the underlying pseudorandom number generator which samples from the standard normal distribution.

    -   [`improved-ziggurat`][@stdlib/random/base/improved-ziggurat]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/improved-ziggurat
    -   [`box-muller`][@stdlib/random/base/box-muller]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/box-muller

    Default: [`'improved-ziggurat'`][@stdlib/random/base/improved-ziggurat].

-   **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 returned pseudorandom number generator, one must seed the provided `prng` (assuming the provided `prng` is seedable).

-   **seed**: pseudorandom number generator seed. Valid seed values vary according to the underlying PRNG.

-   **state**: pseudorandom number generator state. Valid state values vary according to the underlying PRNG. 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 a returned generator has exclusive control over its internal state. Default: `true`.

By default, the underlying pseudorandom number generator is [`improved-ziggurat`][@stdlib/random/base/improved-ziggurat]. To use a different PRNG, set the `name` option.

```javascript
var rand = randn.factory({
    'name': 'box-muller'
});

var r = rand();
// returns <number>
```

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

```javascript
var minstd = require( '@stdlib/random/base/minstd' );

var rand = randn.factory({
    'prng': minstd.normalized
});

var r = rand();
// returns <number>
```

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

```javascript
var rand1 = randn.factory({
    'seed': 12345
});

var r1 = rand1();
// returns <number>

var rand2 = randn.factory({
    'seed': 12345
});

var r2 = rand2();
// returns <number>

var bool = ( r1 === r2 );
// returns true
```

To return a generator having a specific initial state, set the generator `state` option.

```javascript
var rand;
var bool;
var r;
var i;

// Generate pseudorandom numbers, thus progressing the generator state:
for ( i = 0; i < 1000; i++ ) {
    r = randn();
}

// Create a new PRNG initialized to the current state of `randn`:
rand = randn.factory({
    'state': randn.state
});

// Test that the generated pseudorandom numbers are the same:
bool = ( rand() === randn() );
// returns true
```

#### randn.NAME

The generator name.

```javascript
var str = randn.NAME;
// returns 'randn'
```

#### randn.PRNG

The underlying pseudorandom number generator.

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

#### randn.seed

The value used to seed `randn()`.

```javascript
var rand;
var r;
var i;

// Generate pseudorandom values...
for ( i = 0; i < 100; i++ ) {
    r = randn();
}

// Generate the same pseudorandom values...
rand = randn.factory({
    'seed': randn.seed
});
for ( i = 0; i < 100; i++ ) {
    r = rand();
}
```

If provided a PRNG for uniformly distributed numbers, this value is `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

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

#### randn.seedLength

Length of generator seed.

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

If provided a PRNG for uniformly distributed numbers, this value is `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

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

#### randn.state

Writable property for getting and setting the generator state.

```javascript
var r = randn();
// returns <number>

r = randn();
// returns <number>

// ...

// Get a copy of the current state:
var state = randn.state;

r = randn();
// returns <number>

r = randn();
// returns <number>

// Reset the state:
randn.state = state;

// Replay the last two pseudorandom numbers:
r = randn();
// returns <number>

r = randn();
// returns <number>

// ...
```

If provided a PRNG for uniformly distributed numbers, this value is `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

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

#### randn.stateLength

Length of generator state.

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

If provided a PRNG for uniformly distributed numbers, this value is `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

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

#### randn.byteLength

Size (in bytes) of generator state.

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

If provided a PRNG for uniformly distributed numbers, this value is `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

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

#### randn.toJSON()

Serializes the pseudorandom number generator as a JSON object.

```javascript
var o = randn.toJSON();
// returns { 'type': 'PRNG', 'name': '...', 'state': {...}, 'params': [] }
```

If provided a PRNG for uniformly distributed numbers, this method returns `null`.

<!-- eslint-disable stdlib/no-builtin-math -->

```javascript
var rand = randn.factory({
    'prng': Math.random
});

var o = rand.toJSON();
// returns null
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   **Warning**: the default underlying source of pseudorandom numbers may **change** in the future. If exact reproducibility is required, either explicitly specify a PRNG via the `name` option or use an underlying PRNG directly.
-   If PRNG state is "shared" (meaning a state array was provided during PRNG creation and **not** copied) and one sets the generator state to a state array having a different length, the PRNG does **not** update the existing shared state and, instead, points to the newly provided state array. In order to synchronize PRNG output according to the new shared state array, the state array for **each** relevant PRNG must be **explicitly** set.
-   If PRNG state is "shared" and one sets the generator state to a state array of the same length, the PRNG state is updated (along with the state of all other PRNGs sharing the PRNG's state array).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var randn = require( '@stdlib/random/base/randn' );

var seed;
var rand;
var i;

// Generate pseudorandom numbers...
for ( i = 0; i < 100; i++ ) {
    console.log( randn() );
}

// Create a new pseudorandom number generator...
seed = 1234;
rand = randn.factory({
    'seed': seed
});
for ( i = 0; i < 100; i++ ) {
    console.log( rand() );
}

// Create another pseudorandom number generator using a previous seed...
rand = randn.factory({
    'seed': randn.seed
});
for ( i = 0; i < 100; i++ ) {
    console.log( rand() );
}
```

</section>

<!-- /.examples -->

<section class="links">

[@stdlib/random/base/improved-ziggurat]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/improved-ziggurat

[@stdlib/random/base/box-muller]: https://www.npmjs.com/package/@stdlib/random/tree/main/base/box-muller

</section>

<!-- /.links -->