pdf.js (1671B)
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 density function (PDF) for a uniform distribution with minimum support `a` and maximum support `b` at a value `x`. 30 * 31 * @param {number} x - input value 32 * @param {number} a - minimum support 33 * @param {number} b - maximum support 34 * @returns {number} evaluated PDF 35 * 36 * @example 37 * var y = pdf( 2.0, 0.0, 4.0 ); 38 * // returns 0.25 39 * 40 * @example 41 * var y = pdf( 5.0, 0.0, 4.0 ); 42 * // returns 0.0 43 * 44 * @example 45 * var y = pdf( 0.25, 0.0, 1.0 ); 46 * // returns 1.0 47 * 48 * @example 49 * var y = pdf( NaN, 0.0, 1.0 ); 50 * // returns NaN 51 * 52 * @example 53 * var y = pdf( 0.0, NaN, 1.0 ); 54 * // returns NaN 55 * 56 * @example 57 * var y = pdf( 0.0, 0.0, NaN ); 58 * // returns NaN 59 * 60 * @example 61 * var y = pdf( 2.0, 3.0, 1.0 ); 62 * // returns NaN 63 */ 64 function pdf( x, a, b ) { 65 if ( 66 isnan( x ) || 67 isnan( a ) || 68 isnan( b ) || 69 a >= b 70 ) { 71 return NaN; 72 } 73 if ( x < a || x > b ) { 74 return 0.0; 75 } 76 return 1.0 / ( b - a ); 77 } 78 79 80 // EXPORTS // 81 82 module.exports = pdf;