factory.js (1859B)
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 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 26 var PI = require( '@stdlib/constants/float64/pi' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the probability density function (PDF) for an arcsine distribution with minimum support `a` and maximum support `b`. 33 * 34 * @param {number} a - minimum support 35 * @param {number} b - maximum support 36 * @returns {Function} PDF 37 * 38 * @example 39 * var pdf = factory( 0.0, 10.0 ); 40 * var y = pdf( 2.0 ); 41 * // returns ~0.08 42 * 43 * y = pdf( 12.0 ); 44 * // returns 0.0 45 */ 46 function factory( a, b ) { 47 if ( 48 isnan( a ) || 49 isnan( b ) || 50 a >= b 51 ) { 52 return constantFunction( NaN ); 53 } 54 return pdf; 55 56 /** 57 * Evaluates the probability density function (PDF) for an arcsine distribution. 58 * 59 * @private 60 * @param {number} x - input value 61 * @returns {number} evaluated PDF 62 * 63 * @example 64 * var y = pdf( 2.0 ); 65 * // returns <number> 66 */ 67 function pdf( x ) { 68 if ( isnan( x ) ) { 69 return NaN; 70 } 71 if ( x < a || x > b ) { 72 return 0.0; 73 } 74 return 1.0 / ( PI * sqrt( ( x-a ) * ( b-x ) ) ); 75 } 76 } 77 78 79 // EXPORTS // 80 81 module.exports = factory;