time-to-botec

factory.js (7317B)

---

 /**
 * @license Apache-2.0
 *
 * Copyright (c) 2018 The Stdlib Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
 'use strict';
 
 // MODULES //
 
 var setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
 var setReadOnlyAccessor = require( '@stdlib/utils/define-nonenumerable-read-only-accessor' );
 var setReadWriteAccessor = require( '@stdlib/utils/define-nonenumerable-read-write-accessor' );
 var isPositive = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
 var isObject = require( '@stdlib/assert/is-plain-object' );
 var isFunction = require( '@stdlib/assert/is-function' );
 var hasOwnProp = require( '@stdlib/assert/has-own-property' );
 var constantFunction = require( '@stdlib/utils/constant-function' );
 var noop = require( '@stdlib/utils/noop' );
 var randu = require( './../../../base/mt19937' ).factory;
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
 var typedarray2json = require( '@stdlib/array/to-json' );
 var exponential0 = require( './exponential.js' );
 
 
 // MAIN //
 
 /**
 * Returns a pseudorandom number generator for generating exponentially distributed random numbers.
 *
 * @param {PositiveNumber} [lambda] - rate parameter
 * @param {Options} [options] - function options
 * @param {PRNG} [options.prng] - pseudorandom number generator which generates uniformly distributed pseudorandom numbers
 * @param {PRNGSeedMT19937} [options.seed] - pseudorandom number generator seed
 * @param {PRNGStateMT19937} [options.state] - pseudorandom number generator state
 * @param {boolean} [options.copy=true] - boolean indicating whether to copy a provided pseudorandom number generator state
 * @throws {TypeError} `lambda` must be a positive number
 * @throws {TypeError} options argument must be an object
 * @throws {TypeError} must provide valid options
 * @throws {Error} must provide a valid state
 * @returns {PRNG} pseudorandom number generator
 *
 * @example
 * var exponential = factory( 0.5 );
 * var v = exponential();
 * // returns <number>
 *
 * @example
 * var exponential = factory( 0.8, {
 *     'seed': 297
 * });
 * var v = exponential();
 * // returns ~3.735
 *
 * @example
 * var exponential = factory();
 * var v = exponential( 0.5 );
 * // returns <number>
 */
 function factory() {
 	var lambda;
 	var opts;
 	var rand;
 	var prng;
 
 	if ( arguments.length === 0 ) {
 		rand = randu();
 	} else if (
 		arguments.length === 1 &&
 		isObject( arguments[ 0 ] )
 	) {
 		opts = arguments[ 0 ];
 		if ( hasOwnProp( opts, 'prng' ) ) {
 			if ( !isFunction( opts.prng ) ) {
 				throw new TypeError( 'invalid option. `prng` option must be a pseudorandom number generator function. Option: `' + opts.prng + '`.' );
 			}
 			rand = opts.prng;
 		} else {
 			rand = randu( opts );
 		}
 	} else {
 		lambda = arguments[ 0 ];
 		if ( !isPositive( lambda ) ) {
 			throw new TypeError( 'invalid argument. First argument must be a positive number. Value: `' + lambda + '`.' );
 		}
 		if ( arguments.length > 1 ) {
 			opts = arguments[ 1 ];
 			if ( !isObject( opts ) ) {
 				throw new TypeError( 'invalid argument. Options argument must be an object. Value: `' + opts + '`.' );
 			}
 			if ( hasOwnProp( opts, 'prng' ) ) {
 				if ( !isFunction( opts.prng ) ) {
 					throw new TypeError( 'invalid option. `prng` option must be a pseudorandom number generator function. Option: `' + opts.prng + '`.' );
 				}
 				rand = opts.prng;
 			} else {
 				rand = randu( opts );
 			}
 		} else {
 			rand = randu();
 		}
 	}
 	if ( lambda === void 0 ) {
 		prng = exponential2;
 	} else {
 		prng = exponential1;
 	}
 	setReadOnly( prng, 'NAME', 'exponential' );
 
 	// If we are provided an "external" PRNG, we don't support getting or setting PRNG state, as we'd need to check for compatible state value types, etc, entailing considerable complexity.
 	if ( opts && opts.prng ) {
 		setReadOnly( prng, 'seed', null );
 		setReadOnly( prng, 'seedLength', null );
 		setReadWriteAccessor( prng, 'state', constantFunction( null ), noop );
 		setReadOnly( prng, 'stateLength', null );
 		setReadOnly( prng, 'byteLength', null );
 		setReadOnly( prng, 'toJSON', constantFunction( null ) );
 		setReadOnly( prng, 'PRNG', rand );
 	} else {
 		setReadOnlyAccessor( prng, 'seed', getSeed );
 		setReadOnlyAccessor( prng, 'seedLength', getSeedLength );
 		setReadWriteAccessor( prng, 'state', getState, setState );
 		setReadOnlyAccessor( prng, 'stateLength', getStateLength );
 		setReadOnlyAccessor( prng, 'byteLength', getStateSize );
 		setReadOnly( prng, 'toJSON', toJSON );
 		setReadOnly( prng, 'PRNG', rand );
 		rand = rand.normalized;
 	}
 	return prng;
 
 	/**
 	* Returns the PRNG seed.
 	*
 	* @private
 	* @returns {PRNGSeedMT19937} seed
 	*/
 	function getSeed() {
 		return rand.seed;
 	}
 
 	/**
 	* Returns the PRNG seed length.
 	*
 	* @private
 	* @returns {PositiveInteger} seed length
 	*/
 	function getSeedLength() {
 		return rand.seedLength;
 	}
 
 	/**
 	* Returns the PRNG state length.
 	*
 	* @private
 	* @returns {PositiveInteger} state length
 	*/
 	function getStateLength() {
 		return rand.stateLength;
 	}
 
 	/**
 	* Returns the PRNG state size (in bytes).
 	*
 	* @private
 	* @returns {PositiveInteger} state size (in bytes)
 	*/
 	function getStateSize() {
 		return rand.byteLength;
 	}
 
 	/**
 	* Returns the current pseudorandom number generator state.
 	*
 	* @private
 	* @returns {PRNGStateMT19937} current state
 	*/
 	function getState() {
 		return rand.state;
 	}
 
 	/**
 	* Sets the pseudorandom number generator state.
 	*
 	* @private
 	* @param {PRNGStateMT19937} s - generator state
 	* @throws {Error} must provide a valid state
 	*/
 	function setState( s ) {
 		rand.state = s;
 	}
 
 	/**
 	* Serializes the pseudorandom number generator as a JSON object.
 	*
 	* ## Notes
 	*
 	* -   `JSON.stringify()` implicitly calls this method when stringifying a PRNG.
 	*
 	* @private
 	* @returns {Object} JSON representation
 	*/
 	function toJSON() {
 		var out = {};
 		out.type = 'PRNG';
 		out.name = prng.NAME;
 		out.state = typedarray2json( rand.state );
 		if ( lambda === void 0 ) {
 			out.params = [];
 		} else {
 			out.params = [ lambda ];
 		}
 		return out;
 	}
 
 	/**
 	* Returns a pseudorandom number drawn from an exponential distribution with bound parameter `lambda`.
 	*
 	* @private
 	* @returns {NonNegativeNumber} pseudorandom number
 	*
 	* @example
 	* var v = exponential1();
 	* // returns <number>
 	*/
 	function exponential1() {
 		return exponential0( rand, lambda );
 	}
 
 	/**
 	* Returns a pseudorandom number drawn from an exponential distribution with parameter `lambda`.
 	*
 	* @private
 	* @param {PositiveNumber} lambda - rate parameter
 	* @returns {NonNegativeNumber} pseudorandom number
 	*
 	* @example
 	* var v = exponential2( 4.8 );
 	* // returns <number>
 	*/
 	function exponential2( lambda ) {
 		if (
 			isnan( lambda ) ||
 			lambda <= 0.0
 		) {
 			return NaN;
 		}
 		return exponential0( rand, lambda );
 	}
 }
 
 
 // EXPORTS //
 
 module.exports = factory;