Gumbel Random Numbers

Usage

var randomStream = require( '@stdlib/random/streams/gumbel' );

randomStream( mu, beta[, options] )

Returns a readable stream for generating pseudorandom numbers drawn from a Gumbel distribution with parameters mu (mean) and beta (scale).

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

var iStream;
var stream;

function log( chunk, idx ) {
    console.log( chunk.toString() );
    if ( idx === 10 ) {
        stream.destroy();
    }
}

stream = randomStream( -2.0, 2.0 );
iStream = inspectStream( log );

stream.pipe( iStream );

The function accepts the following options:

• objectMode: specifies whether a stream should operate in objectMode. Default: false.
• encoding: specifies how Buffer objects should be decoded to strings. Default: null.
• highWaterMark: specifies the maximum number of bytes to store in an internal buffer before ceasing to generate additional pseudorandom numbers.
• sep: separator used to join streamed data. This option is only applicable when a stream is not in objectMode. Default: '\n'.
• iter: number of iterations.
• 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 stream, 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 and/or streams. Setting this option to true ensures that a stream generator has exclusive control over its internal state. Default: true.
• siter: number of iterations after which to emit the pseudorandom number generator state. This option is useful when wanting to deterministically capture a stream's underlying PRNG state. Default: 1e308.

To set stream options,

var opts = {
    'objectMode': true,
    'encoding': 'utf8',
    'highWaterMark': 64
};

var stream = randomStream( 0.0, 2.0, opts );

By default, the function returns a stream which can generate an infinite number of values (i.e., the stream will never end). To limit the number of generated pseudorandom numbers, set the iter option.

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

function log( chunk ) {
    console.log( chunk.toString() );
}

var opts = {
    'iter': 10
};

var stream = randomStream( 0.0, 1.0, opts );
var iStream = inspectStream( log );

stream.pipe( iStream );

By default, when not operating in objectMode, a returned stream delineates generated pseudorandom numbers using a newline character. To specify an alternative separator, set the sep option.

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

function log( chunk ) {
    console.log( chunk.toString() );
}

var opts = {
    'iter': 10,
    'sep': ','
};

var stream = randomStream( 2.0, 1.0, opts );
var iStream = inspectStream( log );

stream.pipe( iStream );

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

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

function log( v ) {
    console.log( v );
}

var opts = {
    'objectMode': true,
    'iter': 10,
    'seed': 1234
};

var stream = randomStream( 2.0, 1.0, opts );

opts = {
    'objectMode': true
};
var iStream = inspectStream( opts, log );

stream.pipe( iStream );

To return a readable stream with an underlying pseudorandom number generator having a specific initial state, set the state option.

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

function log( v ) {
    console.log( v );
}

var opts1 = {
    'objectMode': true,
    'iter': 10
};

var stream = randomStream( 2.0, 2.0, opts1 );

var opts2 = {
    'objectMode': true
};
var iStream = inspectStream( opts2, log );

// Stream pseudorandom numbers, thus progressing the underlying generator state:
stream.pipe( iStream );

// Create a new PRNG stream initialized to the last state of the previous stream:
var opts3 = {
    'objectMode': true,
    'iter': 10,
    'state': stream.state
};

stream = randomStream( 2.0, 2.0, opts3 );
iStream = inspectStream( opts2, log );

// Stream pseudorandom numbers starting from the last state of the previous stream:
stream.pipe( iStream );

stream.PRNG

The underlying pseudorandom number generator.

var stream = randomStream( 2.0, 2.0 );

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

stream.seed

The value used to seed the underlying pseudorandom number generator.

var stream = randomStream( 2.0, 2.0 );

var seed = stream.seed;
// returns <Uint32Array>

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

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

var stream = randomStream( 2.0, 2.0, {
    'prng': minstd
});

var seed = stream.seed;
// returns null

stream.seedLength

Length of underlying pseudorandom number generator seed.

var stream = randomStream( 2.0, 2.0 );

var len = stream.seedLength;
// returns <number>

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

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

var stream = randomStream( 2.0, 2.0, {
    'prng': minstd
});

var len = stream.seedLength;
// returns null

stream.state

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

var stream = randomStream( 2.0, 2.0 );

var state = stream.state;
// returns <Uint32Array>

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

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

var stream = randomStream( 2.0, 2.0, {
    'prng': minstd
});

var state = stream.state;
// returns null

stream.stateLength

Length of underlying pseudorandom number generator state.

var stream = randomStream( 2.0, 2.0 );

var len = stream.stateLength;
// returns <number>

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

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

var stream = randomStream( 2.0, 2.0, {
    'prng': minstd
});

var len = stream.stateLength;
// returns null

stream.byteLength

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

var stream = randomStream( 2.0, 2.0 );

var sz = stream.byteLength;
// returns <number>

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

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

var stream = randomStream( 2.0, 2.0, {
    'prng': minstd
});

var sz = stream.byteLength;
// returns null

randomStream.factory( [mu, beta, ][options] )

Returns a function for creating readable streams which generate pseudorandom numbers drawn from a Gumbel distribution.

var opts = {
    'objectMode': true,
    'encoding': 'utf8',
    'highWaterMark': 64
};

var createStream = randomStream.factory( opts );

If provided distribution parameters, the returned function returns readable streams which generate pseudorandom numbers drawn from the specified distribution.

var createStream = randomStream.factory( 2.0, 2.0 );

var stream1 = createStream();
var stream2 = createStream();
// ...

If not provided distribution parameters, the returned function requires that distribution parameters be provided at each invocation.

var createStream = randomStream.factory();

var stream1 = createStream( 2.0, 2.0 );
var stream2 = createStream( 2.0, 2.0 );
// ...

The method accepts the same options as randomStream().

randomStream.objectMode( mu, beta[, options] )

This method is a convenience function to create streams which always operate in objectMode.

var inspectStream = require( '@stdlib/streams/node/inspect-sink' );

function log( v ) {
    console.log( v );
}

var opts = {
    'iter': 10
};
var stream = randomStream.objectMode( 2.0, 2.0, opts );

opts = {
    'objectMode': true
};
var iStream = inspectStream( opts, log );

stream.pipe( iStream );

This method accepts the same options as randomStream(); however, the method will always override the objectMode option in options.

Events

In addition to the standard readable stream events, the following events are supported...

'state'

Emitted after internally generating siter pseudorandom numbers.

var opts = {
    'siter': 10 // emit the PRNG state every 10 pseudorandom numbers
};

var stream = randomStream( 2.0, 2.0, opts );

stream.on( 'state', onState );

function onState( state ) {
    // Do something with the emitted state, such as save to file...
}