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