Usage

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

#### exponential( lambda )

Returns a pseudorandom number drawn from an [exponential][exponential] distribution with rate parameter lambda.

`javascript
var r = exponential( 7.9 );
// returns
`

If lambda <= 0 or lambda is NaN, the function returns NaN.

`javascript
var r = exponential( -2.0 );
// returns NaN

r = exponential( NaN );
// returns NaN
`

#### exponential.factory( \[lambda, ]\[options] )

Returns a pseudorandom number generator (PRNG) for generating pseudorandom numbers drawn from an [exponential][exponential] distribution.

`javascript
var rand = exponential.factory();

var r = rand( 5.0 );
// returns
`

If provided lambda, the returned generator returns random variates from the specified distribution.

`javascript
var rand = exponential.factory( 10.0 );

var r = rand();
// returns

r = rand();
// returns
`

If not provided lambda, the returned generator requires that lambda be provided at each invocation.

`javascript
var rand = exponential.factory();

var r = rand( 4.0 );
// returns

r = rand( 3.14 );
// returns
`

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 returned 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 a returned 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 rand = exponential.factory({
'prng': minstd.normalized
});

var r = rand( 3.0 );
// returns
`

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

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

var r1 = rand1( 3.0 );
// returns

var rand2 = exponential.factory( 3.0, {
'seed': 12345
});

var r2 = rand2();
// returns

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 = exponential( 3.0 );
}

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

// Test that the generated pseudorandom numbers are the same:
bool = ( rand( 3.0 ) === exponential( 3.0 ) );
// returns true
`

#### exponential.NAME

The generator name.

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

#### exponential.PRNG

The underlying pseudorandom number generator.

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

#### exponential.seed

The value used to seed exponential().

`javascript
var rand;
var r;
var i;

// Generate pseudorandom values...
for ( i = 0; i < 100; i++ ) {
r = exponential( 2.0 );
}

// Generate the same pseudorandom values...
rand = exponential.factory( 2.0, {
'seed': exponential.seed
});
for ( i = 0; i < 100; i++ ) {
r = rand();
}
`

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

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

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

#### exponential.seedLength

Length of generator seed.

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

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

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

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

#### exponential.state

Writable property for getting and setting the generator state.

`javascript
var r = exponential( 7.9 );
// returns

r = exponential( 7.9 );
// returns

// ...

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

r = exponential( 7.9 );
// returns

r = exponential( 7.9 );
// returns

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

// Replay the last two pseudorandom numbers:
r = exponential( 7.9 );
// returns

r = exponential( 7.9 );
// returns

// ...
`

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

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

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

#### exponential.stateLength

Length of generator state.

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

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

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

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

#### exponential.byteLength

Size (in bytes) of generator state.

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

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

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

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

#### exponential.toJSON()

Serializes the pseudorandom number generator as a JSON object.

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

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

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

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