81 lines
1.9 KiB
JavaScript
81 lines
1.9 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var hin = require( './hin.js' );
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// MAIN //
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/**
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* Returns a pseudorandom number drawn from a hypergeometric distribution.
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*
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* ## References
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*
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* - Kachitvichyanukul, Voratas., and Burce Schmeiser. 1985. "Computer generation of hypergeometric random variates." _Journal of Statistical Computation and Simulation_ 22 (2): 127–45. doi:[10.1080/00949658508810839][@kachitvichyanukul:1985].
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*
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* [@kachitvichyanukul:1985]: http://dx.doi.org/10.1080/00949658508810839
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*
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*
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* @private
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* @param {PRNG} rand - PRNG for uniformly distributed numbers
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* @param {NonNegativeInteger} N - population size
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* @param {NonNegativeInteger} K - subpopulation size
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* @param {NonNegativeInteger} n - number of draws
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* @returns {NonNegativeInteger} pseudorandom number
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*/
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function hypergeometric( rand, N, K, n ) {
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var n1;
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var n2;
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var k;
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var x;
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if ( n > N/2 ) {
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k = N - n;
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if ( 2*K <= N ) {
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n1 = K;
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n2 = N - K;
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x = hin( rand, n1, n2, k );
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return K - x;
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}
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n2 = K;
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n1 = N - K;
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x = hin( rand, n1, n2, k );
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return n - N + K + x;
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}
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k = n;
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if ( 2*K <= N ) {
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n1 = K;
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n2 = N - K;
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x = hin( rand, n1, n2, k );
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return x;
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}
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n1 = N - K;
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n2 = K;
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x = hin( rand, n1, n2, k );
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return n - x;
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}
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// EXPORTS //
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module.exports = hypergeometric;
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