logpdf.js (1541B)
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 PINF = require( '@stdlib/constants/float64/pinf' ); 24 var NINF = require( '@stdlib/constants/float64/ninf' ); 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 27 28 // MAIN // 29 30 /** 31 * Evaluates the natural logarithm of the probability density function (logPDF) for a degenerate distribution centered at `mu`. 32 * 33 * @param {number} x - input value 34 * @param {number} mu - constant value of the distribution 35 * @returns {number} natural logarithm of probability density function 36 * 37 * @example 38 * var y = logpdf( 2.0, 3.0 ); 39 * // returns -Infinity 40 * 41 * @example 42 * var y = logpdf( 3.0, 3.0 ); 43 * // returns Infinity 44 * 45 * @example 46 * var y = logpdf( NaN, 0.0 ); 47 * // returns NaN 48 * 49 * @example 50 * var y = logpdf( 0.0, NaN ); 51 * // returns NaN 52 */ 53 function logpdf( x, mu ) { 54 if ( isnan( x ) || isnan( mu ) ) { 55 return NaN; 56 } 57 return ( x === mu ) ? PINF : NINF; 58 } 59 60 61 // EXPORTS // 62 63 module.exports = logpdf;