factory.js (1689B)
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 constantFunction = require( '@stdlib/utils/constant-function' ); 24 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 26 27 // MAIN // 28 29 /** 30 * Returns a function for evaluating the probability mass function (PMF) for a Bernoulli distribution with success probability `p`. 31 * 32 * @param {Probability} p - success probability 33 * @returns {Function} PMF 34 * 35 * @example 36 * var pmf = factory( 0.8 ); 37 * var y = pmf( 0.0 ); 38 * // returns 0.2 39 * 40 * y = pmf( 1.0 ); 41 * // returns 0.8 42 */ 43 function factory( p ) { 44 if ( 45 isnan( p ) || 46 p < 0.0 || 47 p > 1.0 48 ) { 49 return constantFunction( NaN ); 50 } 51 return pmf; 52 53 /** 54 * Evaluates the probability mass function (PMF) for a Bernoulli distribution. 55 * 56 * @private 57 * @param {number} x - input value 58 * @returns {Probability} evaluated PMF 59 * 60 * @example 61 * var y = pmf( 2.0 ); 62 * // returns <number> 63 */ 64 function pmf( x ) { 65 if ( isnan( x ) ) { 66 return NaN; 67 } 68 if ( x === 0.0 ) { 69 return 1.0 - p; 70 } 71 if ( x === 1.0 ) { 72 return p; 73 } 74 return 0.0; 75 } 76 } 77 78 79 // EXPORTS // 80 81 module.exports = factory;