factory.js (1942B)
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 PINF = require( '@stdlib/constants/float64/pinf' ); 25 var NINF = require( '@stdlib/constants/float64/ninf' ); 26 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the natural logarithm of the probability density function (logPDF) of a degenerate distribution centered at a provided mean value. 33 * 34 * @param {number} mu - value at which to center the distribution 35 * @returns {Function} function to evaluate the natural logarithm of the probability density function 36 * 37 * @example 38 * var logpdf = factory( 5.0 ); 39 * 40 * var y = logpdf( 0.0 ); 41 * // returns -Infinity 42 * 43 * y = logpdf( 5.0 ); 44 * // returns Infinity 45 */ 46 function factory( mu ) { 47 if ( isnan( mu ) ) { 48 return constantFunction( NaN ); 49 } 50 return logpdf; 51 52 /** 53 * Evaluates the natural logarithm of the probability density function (logPDF) of a degenerate distribution. 54 * 55 * @private 56 * @param {number} x - input value 57 * @returns {number} natural logarithm of the probability density function 58 * 59 * @example 60 * var y = logpdf( 10.0 ); 61 * // returns <number> 62 */ 63 function logpdf( x ) { 64 if ( isnan( x ) ) { 65 return NaN; 66 } 67 return ( x === mu ) ? PINF : NINF; 68 } 69 } 70 71 72 // EXPORTS // 73 74 module.exports = factory;