pmf.js (1787B)
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 isInteger = require( '@stdlib/math/base/assert/is-integer' ); 24 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 26 27 // MAIN // 28 29 /** 30 * Evaluates the probability mass function (PMF) for a discrete uniform distribution with minimum support `a` and maximum support `b` at a value `x`. 31 * 32 * @param {number} x - input value 33 * @param {integer} a - minimum support 34 * @param {integer} b - maximum support 35 * @returns {number} evaluated PMF 36 * 37 * @example 38 * var y = pmf( 2.0, 0, 4 ); 39 * // returns ~0.2 40 * 41 * @example 42 * var y = pmf( 5.0, 0, 4 ); 43 * // returns 0.0 44 * 45 * @example 46 * var y = pmf( 2, 0, 8 ); 47 * // returns ~0.111 48 * 49 * @example 50 * var y = pmf( NaN, 0, 1 ); 51 * // returns NaN 52 * 53 * @example 54 * var y = pmf( 0.0, NaN, 1 ); 55 * // returns NaN 56 * 57 * @example 58 * var y = pmf( 0.0, 0, NaN ); 59 * // returns NaN 60 * 61 * @example 62 * var y = pmf( 2.0, 3, 1 ); 63 * // returns NaN 64 */ 65 function pmf( x, a, b ) { 66 if ( 67 isnan( x ) || 68 isnan( a ) || 69 isnan( b ) || 70 !isInteger( a ) || 71 !isInteger( b ) || 72 a > b 73 ) { 74 return NaN; 75 } 76 if ( x < a || x > b || !isInteger( x ) ) { 77 return 0.0; 78 } 79 return 1.0 / ( b - a + 1.0 ); 80 } 81 82 83 // EXPORTS // 84 85 module.exports = pmf;