factory.js (1990B)
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 ln = require( '@stdlib/math/base/special/ln' ); 26 var LN_PI = require( '@stdlib/constants/float64/ln-pi' ); 27 var NINF = require( '@stdlib/constants/float64/ninf' ); 28 29 30 // MAIN // 31 32 /** 33 * Returns a function for evaluating the logarithm of the probability density function (PDF) for an arcsine distribution with minimum support `a` and maximum support `b`. 34 * 35 * @param {number} a - minimum support 36 * @param {number} b - maximum support 37 * @returns {Function} logPDF 38 * 39 * @example 40 * var logpdf = factory( 0.0, 10.0 ); 41 * var y = logpdf( 2.0 ); 42 * // returns ~-2.531 43 * 44 * y = logpdf( 12.0 ); 45 * // returns -Infinity 46 */ 47 function factory( a, b ) { 48 if ( 49 isnan( a ) || 50 isnan( b ) || 51 a >= b 52 ) { 53 return constantFunction( NaN ); 54 } 55 return logpdf; 56 57 /** 58 * Evaluates the logarithm of the probability density function (PDF) for an arcsine distribution. 59 * 60 * @private 61 * @param {number} x - input value 62 * @returns {number} evaluated logPDF 63 * 64 * @example 65 * var y = logpdf( 2.0 ); 66 * // returns <number> 67 */ 68 function logpdf( x ) { 69 if ( isnan( x ) ) { 70 return NaN; 71 } 72 if ( x < a || x > b ) { 73 return NINF; 74 } 75 return -( LN_PI + ( ln( ( x-a ) * ( b-x ) ) / 2.0 ) ); 76 } 77 } 78 79 80 // EXPORTS // 81 82 module.exports = factory;