factory.js (2013B)
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 PI = require( '@stdlib/constants/float64/pi' ); 28 29 30 // VARIABLES // 31 32 var TWO_OVER_PI = 2.0 / PI; 33 34 35 // MAIN // 36 37 /** 38 * Returns a function for evaluating the cumulative distribution function (CDF) for an arcsine distribution with minimum support `a` and maximum support `b`. 39 * 40 * @param {number} a - minimum support 41 * @param {number} b - maximum support 42 * @returns {Function} CDF 43 * 44 * @example 45 * var cdf = factory( 0.0, 10.0 ); 46 * var y = cdf( 0.5 ); 47 * // returns ~0.144 48 * 49 * y = cdf( 8.0 ); 50 * // returns ~0.705 51 */ 52 function factory( a, b ) { 53 if ( 54 isnan( a ) || 55 isnan( b ) || 56 a >= b 57 ) { 58 return constantFunction( NaN ); 59 } 60 return cdf; 61 62 /** 63 * Evaluates the cumulative distribution function (CDF) for an arcsine distribution. 64 * 65 * @private 66 * @param {number} x - input value 67 * @returns {Probability} evaluated CDF 68 * 69 * @example 70 * var y = cdf( 2.0 ); 71 * // returns <number> 72 */ 73 function cdf( x ) { 74 if ( isnan( x ) ) { 75 return NaN; 76 } 77 if ( x < a ) { 78 return 0.0; 79 } 80 if ( x >= b ) { 81 return 1.0; 82 } 83 return TWO_OVER_PI * asin( sqrt( ( x-a ) / ( b-a ) ) ); 84 } 85 } 86 87 88 // EXPORTS // 89 90 module.exports = factory;