factory.js (2021B)
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 isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' ); 24 var constantFunction = require( '@stdlib/utils/constant-function' ); 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var exp = require( '@stdlib/math/base/special/exp' ); 27 var pow = require( '@stdlib/math/base/special/pow' ); 28 var PINF = require( '@stdlib/constants/float64/pinf' ); 29 30 31 // MAIN // 32 33 /** 34 * Returns a function for evaluating the moment-generating function (MGF) of a binomial distribution with number of trials `n` and success probability `p`. 35 * 36 * @param {NonNegativeInteger} n - number of trials 37 * @param {Probability} p - success probability 38 * @returns {Function} MGF 39 * 40 * @example 41 * var mgf = factory( 10, 0.5 ); 42 * var y = mgf( 0.3 ); 43 * // returns ~5.013 44 */ 45 function factory( n, p ) { 46 if ( isnan( n ) || 47 isnan( p ) || 48 p < 0.0 || 49 p > 1.0 || 50 !isNonNegativeInteger( n ) || 51 n === PINF 52 ) { 53 return constantFunction( NaN ); 54 } 55 return mgf; 56 57 /** 58 * Evaluates the moment-generating function (MGF) for a binomial distribution. 59 * 60 * @private 61 * @param {number} t - input value 62 * @returns {number} evaluated MGF 63 * 64 * @example 65 * var y = mgf( 0.5 ); 66 * // returns <number> 67 */ 68 function mgf( t ) { 69 var base; 70 if ( isnan( t ) ) { 71 return NaN; 72 } 73 base = 1.0 - p + (p * exp(t)); 74 return pow( base, n ); 75 } 76 } 77 78 79 // EXPORTS // 80 81 module.exports = factory;