factory.js (2212B)
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 betaFactory = require( './../../../../../base/dists/beta/logcdf' ).factory; 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var NINF = require( '@stdlib/constants/float64/ninf' ); 27 var PINF = require( '@stdlib/constants/float64/pinf' ); 28 29 30 // MAIN // 31 32 /** 33 * Returns a function for evaluating the natural logarithm of the cumulative distribution function (CDF) for a beta prime distribution with first shape parameter `alpha` and second shape parameter `beta`. 34 * 35 * @param {PositiveNumber} alpha - first shape parameter 36 * @param {PositiveNumber} beta - second shape parameter 37 * @returns {Function} logCDF 38 * 39 * @example 40 * var logcdf = factory( 0.5, 0.5 ); 41 * 42 * var y = logcdf( 0.8 ); 43 * // returns ~-0.767 44 * 45 * y = logcdf( 0.3 ); 46 * // returns ~-1.143 47 */ 48 function factory( alpha, beta ) { 49 var betaLogCDF; 50 if ( 51 isnan( alpha ) || 52 isnan( beta ) || 53 alpha <= 0.0 || 54 beta <= 0.0 55 ) { 56 return constantFunction( NaN ); 57 } 58 betaLogCDF = betaFactory( alpha, beta ); 59 return logcdf; 60 61 /** 62 * Evaluates the natural logarithm of the cumulative distribution function (CDF) for a beta prime distribution. 63 * 64 * @private 65 * @param {number} x - input value 66 * @returns {number} evaluated logCDF 67 * 68 * @example 69 * var y = logcdf( 2.0 ); 70 * // returns <number> 71 */ 72 function logcdf( x ) { 73 if ( isnan( x ) ) { 74 return NaN; 75 } 76 if ( x <= 0.0 ) { 77 return NINF; 78 } 79 if ( x === PINF ) { 80 return 0.0; 81 } 82 return betaLogCDF( x / ( 1.0 + x ) ); 83 } 84 } 85 86 87 // EXPORTS // 88 89 module.exports = factory;