factory.js (2198B)
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 asin = require( '@stdlib/math/base/special/asin' ); 26 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 27 var ln = require( '@stdlib/math/base/special/ln' ); 28 var LN_PI = require( '@stdlib/constants/float64/ln-pi' ); 29 var NINF = require( '@stdlib/constants/float64/ninf' ); 30 var LN2 = require( '@stdlib/constants/float64/ln-two' ); 31 32 33 // MAIN // 34 35 /** 36 * Returns a function for evaluating the logarithm of the cumulative distribution function (CDF) for an arcsine distribution with minimum support `a` and maximum support `b`. 37 * 38 * @param {number} a - minimum support 39 * @param {number} b - maximum support 40 * @returns {Function} logCDF 41 * 42 * @example 43 * var logcdf = factory( 0.0, 10.0 ); 44 * var y = logcdf( 0.5 ); 45 * // returns ~-1.941 46 * 47 * y = logcdf( 8.0 ); 48 * // returns ~-0.35 49 */ 50 function factory( a, b ) { 51 if ( 52 isnan( a ) || 53 isnan( b ) || 54 a >= b 55 ) { 56 return constantFunction( NaN ); 57 } 58 return logcdf; 59 60 /** 61 * Evaluates the logarithm of the cumulative distribution function (CDF) for an arcsine distribution. 62 * 63 * @private 64 * @param {number} x - input value 65 * @returns {number} evaluated logCDF 66 * 67 * @example 68 * var y = logcdf( 2.0 ); 69 * // returns <number> 70 */ 71 function logcdf( x ) { 72 if ( isnan( x ) ) { 73 return NaN; 74 } 75 if ( x < a ) { 76 return NINF; 77 } 78 if ( x >= b ) { 79 return 0.0; 80 } 81 return LN2 - LN_PI + ln( asin( sqrt( ( x-a ) / ( b-a ) ) ) ); 82 } 83 } 84 85 86 // EXPORTS // 87 88 module.exports = factory;