Usage

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

#### poisson( shape, lambda\[, options] )

Returns an [ndarray][@stdlib/ndarray/ctor] containing pseudorandom numbers drawn from a [Poisson][@stdlib/random/base/poisson] distribution.

`javascript
var arr = poisson( [ 3, 3 ], 2.0 );
// returns
`

The function has the following parameters:

- shape: output shape.
- lambda: mean parameter. May be either a scalar or an [ndarray][@stdlib/ndarray/ctor]. When providing an [ndarray][@stdlib/ndarray/ctor], the [ndarray][@stdlib/ndarray/ctor] must be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the specified output shape.
- options: function options.

When provided a scalar distribution parameter, every element in the output [ndarray][@stdlib/ndarray/ctor] is drawn from the same distribution. To generate pseudorandom numbers drawn from different distributions, provide a distribution parameter argument as an [ndarray][@stdlib/ndarray/ctor]. The following example demonstrates broadcasting an [ndarray][@stdlib/ndarray/ctor] containing distribution parameters to generate sub-matrices drawn from different distributions.

`javascript
var getShape = require( '@stdlib/ndarray-shape' );
var array = require( '@stdlib/ndarray-array' );

var lambda = array( [ [ [ 2.0 ] ], [ [ 10.0 ] ] ] );
// returns

var shape = getShape( lambda );
// returns [ 2, 1, 1 ]

var arr = poisson( [ 2, 3, 3 ], lambda );
// returns
`

If provided an empty shape, the function returns a zero-dimensional [ndarray][@stdlib/ndarray/ctor].

`javascript
var getShape = require( '@stdlib/ndarray-shape' );

var arr = poisson( [], 2.0 );
// returns

var shape = getShape( arr );
// returns []

var v = arr.get();
// returns
`

The function accepts the following options:

- dtype: output ndarray data type. Must be a real or "generic" [data type][@stdlib/ndarray/dtypes].
- order: ndarray order (i.e., memory layout), which is either row-major (C-style) or column-major (Fortran-style). Default: 'row-major'.
- mode: specifies how to handle indices which exceed ndarray dimensions. For a list of supported modes, see [ndarray][@stdlib/ndarray/ctor]. Default: 'throw'.
- submode: a mode array which specifies for each dimension how to handle subscripts which exceed ndarray dimensions. If provided fewer modes than dimensions, an [ndarray][@stdlib/ndarray/ctor] instance recycles modes using modulo arithmetic. Default: [ options.mode ].
- readonly: boolean indicating whether an ndarray should be read-only. Default: false.

By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a [data type][@stdlib/ndarray/dtypes] determined by the function's output data type [policy][@stdlib/ndarray/output-dtype-policies]. To override the default behavior, set the dtype option.

`javascript
var getDType = require( '@stdlib/ndarray-dtype' );

var opts = {
'dtype': 'generic'
};

var arr = poisson( [ 3, 3 ], 2.0, opts );
// returns

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

#### poisson.assign( lambda, out )

Fills an [ndarray][@stdlib/ndarray/ctor] with pseudorandom numbers drawn from a [Poisson][@stdlib/random/base/poisson] distribution.

`javascript
var zeros = require( '@stdlib/ndarray-zeros' );

var out = zeros( [ 3, 3 ] );
// returns

var v = poisson.assign( 2.0, out );
// returns

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

The method has the following parameters:

- lambda: mean parameter. May be either a scalar or an [ndarray][@stdlib/ndarray/ctor]. When providing an [ndarray][@stdlib/ndarray/ctor], the [ndarray][@stdlib/ndarray/ctor] must be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the output [ndarray][@stdlib/ndarray/ctor].
- out: output [ndarray][@stdlib/ndarray/ctor].

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

Returns a function for generating pseudorandom numbers drawn from a [Poisson][@stdlib/random/base/poisson] distribution.

`javascript
var getShape = require( '@stdlib/ndarray-shape' );

var random = poisson.factory();

var out = random( [ 3, 3 ], 2.0 );
// returns

var sh = getShape( out );
// returns [ 3, 3 ]
`

The method 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 minstd = require( '@stdlib/random-base-minstd' );

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

var out = random( [ 3, 3 ], 2.0 );
// returns
`

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

`javascript
var opts = {
'seed': 12345
};
var random = poisson.factory( opts );

var out = random( [ 3, 3 ], 2.0 );
// returns
`

The function returned by the factory method has the same interface and accepts the same options as the poisson function above.

#### poisson.PRNG

The underlying pseudorandom number generator.

`javascript
var prng = poisson.PRNG;
// returns
`

#### poisson.seed

The value used to seed the underlying pseudorandom number generator.

`javascript
var seed = poisson.seed;
// returns
`

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 = poisson.factory({
'prng': minstd
});

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

#### poisson.seedLength

Length of underlying pseudorandom number generator seed.

`javascript
var len = poisson.seedLength;
// returns
`

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 = poisson.factory({
'prng': minstd
});

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

#### poisson.state

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

`javascript
var state = poisson.state;
// returns
`

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 = poisson.factory({
'prng': minstd
});

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

#### poisson.stateLength

Length of underlying pseudorandom number generator state.

`javascript
var len = poisson.stateLength;
// returns
`

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 = poisson.factory({
'prng': minstd
});

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

#### poisson.byteLength

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

`javascript
var sz = poisson.byteLength;
// returns
`

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 = poisson.factory({
'prng': minstd
});

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