factory.js (1854B)
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 NINF = require( '@stdlib/constants/float64/ninf' ); 26 27 28 // MAIN // 29 30 /** 31 * Returns a function for evaluating the natural logarithm of the cumulative distribution function (logCDF) of a degenerate distribution centered at a provided mean value. 32 * 33 * @param {number} mu - value at which to center the distribution 34 * @returns {Function} logCDF 35 * 36 * @example 37 * var logcdf = factory( 5.0 ); 38 * 39 * var y = logcdf( 3.0 ); 40 * // returns -Infinity 41 * 42 * y = logcdf( 6.0 ); 43 * // returns 0.0 44 * 45 * y = logcdf( NaN ); 46 * // returns NaN 47 */ 48 function factory( mu ) { 49 if ( isnan( mu ) ) { 50 return constantFunction( NaN ); 51 } 52 return logcdf; 53 54 /** 55 * Evaluates the natural logarithm of the cumulative distribution function (logCDF) of a degenerate distribution. 56 * 57 * @private 58 * @param {number} x - input value 59 * @returns {number} natural logarithm of cumulative distribution function 60 * 61 * @example 62 * var y = logcdf( 10.0 ); 63 * // returns <number> 64 */ 65 function logcdf( x ) { 66 if ( isnan( x ) ) { 67 return NaN; 68 } 69 return ( x < mu ) ? NINF : 0.0; 70 } 71 } 72 73 74 // EXPORTS // 75 76 module.exports = factory;