pmf.js (1745B)
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 isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' ); 24 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 var pow = require( '@stdlib/math/base/special/pow' ); 26 27 28 // MAIN // 29 30 /** 31 * Evaluates the probability mass function (PMF) for a geometric distribution with success probability `p` at a value `x`. 32 * 33 * @param {number} x - input value 34 * @param {Probability} p - success probability 35 * @returns {Probability} evaluated PMF 36 * 37 * @example 38 * var y = pmf( 4.0, 0.3 ); 39 * // returns ~0.072 40 * 41 * @example 42 * var y = pmf( 2.0, 0.7 ); 43 * // returns ~0.063 44 * 45 * @example 46 * var y = pmf( -1.0, 0.5 ); 47 * // returns 0.0 48 * 49 * @example 50 * var y = pmf( 0.0, NaN ); 51 * // returns NaN 52 * 53 * @example 54 * var y = pmf( NaN, 0.5 ); 55 * // returns NaN 56 * 57 * @example 58 * // Invalid success probability: 59 * var y = pmf( 2.0, 1.5 ); 60 * // returns NaN 61 */ 62 function pmf( x, p ) { 63 var q; 64 if ( 65 isnan( x ) || 66 isnan( p ) || 67 p < 0.0 || 68 p > 1.0 69 ) { 70 return NaN; 71 } 72 if ( isNonNegativeInteger( x ) ) { 73 q = 1.0 - p; 74 return p * pow( q, x ); 75 } 76 return 0.0; 77 } 78 79 80 // EXPORTS // 81 82 module.exports = pmf;