factory.js (1669B)
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 26 27 // MAIN // 28 29 /** 30 * Returns a function for evaluating the probability mass function (PMF) of a degenerate distribution centered at a provided mean value. 31 * 32 * @param {number} mu - value at which to center the distribution 33 * @returns {Function} function to evaluate the probability mass function 34 * 35 * @example 36 * var pmf = factory( 5.0 ); 37 * 38 * var y = pmf( 0.0 ); 39 * // returns 0.0 40 * 41 * y = pmf( 5.0 ); 42 * // returns 1.0 43 */ 44 function factory( mu ) { 45 if ( isnan( mu ) ) { 46 return constantFunction( NaN ); 47 } 48 return pmf; 49 50 /** 51 * Evaluates the probability mass function (PMF) of a degenerate distribution. 52 * 53 * @private 54 * @param {number} x - input value 55 * @returns {number} evaluated PMF 56 * 57 * @example 58 * var y = pmf( 10.0 ); 59 * // returns <number> 60 */ 61 function pmf( x ) { 62 if ( isnan( x ) ) { 63 return NaN; 64 } 65 return ( x === mu ) ? 1.0 : 0.0; 66 } 67 } 68 69 70 // EXPORTS // 71 72 module.exports = factory;