Exponential Random Numbers

Usage

var exponential = require( '@stdlib/random/strided/exponential' );

exponential( N, lambda, sl, out, so )

Fills a strided array with pseudorandom numbers drawn from an exponential distribution.

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

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

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

The function has the following parameters:

• N: number of indexed elements.
• lambda: rate parameter.
• sl: index increment for lambda.
• 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,

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

exponential( 3, [ 2.0 ], 0, out, 2 );

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

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

// Initial array:
var lambda0 = new Float64Array( [ 2.0, 2.0, 2.0, 2.0, 2.0, 2.0 ] );

// Create offset view:
var lambda1 = new Float64Array( lambda0.buffer, lambda0.BYTES_PER_ELEMENT*3 ); // start at 4th element

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

// Fill the output array:
exponential( out.length, lambda1, -1, out, 1 );

exponential.ndarray( N, lambda, sl, ol, out, so, oo )

Fills a strided array with pseudorandom numbers drawn from an exponential distribution using alternative indexing semantics.

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

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

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

The function has the following additional parameters:

• ol: starting index for lambda.
• oo: starting index for out.

While 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,

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

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

exponential.factory( [options] )

Returns a function for filling strided arrays with pseudorandom numbers drawn from an exponential distribution.

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

var random = exponential.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 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.

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

var opts = {
    'prng': minstd.normalized
};
var random = exponential.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.

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

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

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

random.PRNG

The underlying pseudorandom number generator.

var prng = exponential.PRNG;
// returns <Function>

exponential.seed

The value used to seed the underlying pseudorandom number generator.

var seed = exponential.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.

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

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

var seed = random.seed;
// returns null

exponential.seedLength

Length of underlying pseudorandom number generator seed.

var len = exponential.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.

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

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

var len = random.seedLength;
// returns null

exponential.state

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

var state = exponential.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.

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

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

var state = random.state;
// returns null

exponential.stateLength

Length of underlying pseudorandom number generator state.

var len = exponential.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.

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

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

var len = random.stateLength;
// returns null

exponential.byteLength

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

var sz = exponential.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.

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

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

var sz = random.byteLength;
// returns null