triangular.js (1365B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 24 25 26 // MAIN // 27 28 /** 29 * Returns a pseudorandom number drawn from a triangular distribution with minimum support `a`, maximum support `b` and mode `c`. 30 * 31 * @private 32 * @param {PRNG} rand - PRNG for generating uniformly distributed numbers 33 * @param {number} a - minimum support 34 * @param {number} b - maximum support 35 * @param {number} c - mode 36 * @returns {number} pseudorandom number 37 */ 38 function triangular( rand, a, b, c ) { 39 var fc; 40 var x; 41 var u; 42 fc = (c - a) / (b - a); 43 u = rand(); 44 if ( u < fc ) { 45 x = (b - a) * (c - a); 46 return a + sqrt( x * u ); 47 } 48 x = (b - a) * (b - c); 49 return b - sqrt( x * (1.0 - u) ); 50 } 51 52 53 // EXPORTS // 54 55 module.exports = triangular;