pmf.js (1641B)
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 isnan = require( '@stdlib/math/base/assert/is-nan' ); 24 25 26 // MAIN // 27 28 /** 29 * Evaluates the probability mass function (PMF) for a Bernoulli distribution with success probability `p` at a value `x`. 30 * 31 * @param {number} x - input value 32 * @param {Probability} p - success probability 33 * @returns {Probability} evaluated PMF 34 * 35 * @example 36 * var y = pmf( 1.0, 0.3 ); 37 * // returns 0.3 38 * 39 * @example 40 * var y = pmf( 0.0, 0.3 ); 41 * // returns 0.7 42 * 43 * @example 44 * var y = pmf( -1.0, 0.5 ); 45 * // returns 0.0 46 * 47 * @example 48 * var y = pmf( 0.8, 0.5 ); 49 * // returns 0.0 50 * 51 * @example 52 * var y = pmf( 0.0, NaN ); 53 * // returns NaN 54 * 55 * @example 56 * var y = pmf( NaN, 0.5 ); 57 * // returns NaN 58 * 59 * @example 60 * // Invalid success probability: 61 * var y = pmf( 1.0, 1.5 ); 62 * // returns NaN 63 */ 64 function pmf( x, p ) { 65 if ( 66 isnan( x ) || 67 isnan( p ) || 68 p < 0.0 || 69 p > 1.0 70 ) { 71 return NaN; 72 } 73 if ( x === 0.0 ) { 74 return 1.0 - p; 75 } 76 if ( x === 1.0 ) { 77 return p; 78 } 79 return 0.0; 80 } 81 82 83 // EXPORTS // 84 85 module.exports = pmf;