factory.js (2651B)
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 isnan = require( '@stdlib/math/base/assert/is-nan' ); 25 var constantFunction = require( '@stdlib/utils/constant-function' ); 26 var exp = require( '@stdlib/math/base/special/exp' ); 27 var fln = require( '@stdlib/math/base/special/factorialln' ); 28 var max = require( '@stdlib/math/base/special/max' ); 29 var min = require( '@stdlib/math/base/special/min' ); 30 var PINF = require( '@stdlib/constants/float64/pinf' ); 31 32 33 // MAIN // 34 35 /** 36 * Returns a function for evaluating the probability mass function (PMF) for a hypergeometric distribution with population size `N`, subpopulation size `K`, and number of draws `n`. 37 * 38 * @param {NonNegativeInteger} N - population size 39 * @param {NonNegativeInteger} K - subpopulation size 40 * @param {NonNegativeInteger} n - number of draws 41 * @returns {Function} PMF 42 * 43 * @example 44 * var mypmf = factory( 30, 20, 5 ); 45 * var y = mypmf( 4.0 ); 46 * // returns ~0.34 47 * 48 * y = mypmf( 1.0 ); 49 * // returns ~0.029 50 */ 51 function factory( N, K, n ) { 52 var maxs; 53 var mins; 54 if ( 55 isnan( N ) || 56 isnan( K ) || 57 isnan( n ) || 58 !isNonNegativeInteger( N ) || 59 !isNonNegativeInteger( K ) || 60 !isNonNegativeInteger( n ) || 61 N === PINF || 62 K === PINF || 63 K > N || 64 n > N 65 ) { 66 return constantFunction( NaN ); 67 } 68 69 mins = max( 0, n + K - N ); 70 maxs = min( K, n ); 71 return pmf; 72 73 /** 74 * Evaluates the probability mass function (PMF) for a hypergeometric distribution. 75 * 76 * @private 77 * @param {number} x - input value 78 * @returns {Probability} evaluated PMF 79 */ 80 function pmf( x ) { 81 var ldenom; 82 var lnum; 83 var lpmf; 84 if ( isnan( x ) ) { 85 return NaN; 86 } 87 if ( 88 isNonNegativeInteger( x ) && 89 mins <= x && 90 x <= maxs 91 ) { 92 lnum = fln( n ) + fln( K ) + fln( N - n ) + fln( N - K ); 93 ldenom = fln( N ) + fln( x ) + fln( n - x ); 94 ldenom += fln( K - x ) + fln( N - K + x - n ); 95 lpmf = lnum - ldenom; 96 return exp( lpmf ); 97 } 98 return 0.0; 99 } 100 } 101 102 103 // EXPORTS // 104 105 module.exports = factory;