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 pow = require( '@stdlib/math/base/special/pow' );
var ln = require( '@stdlib/math/base/special/ln' );
// MAIN //
/**
* Handles case where both `alpha` and `beta` are greater than `1.0`.
*
* @private
* @param {PRNG} randu - PRNG for uniformly distributed numbers
* @param {PRNG} randn - PRNG for normally distributed numbers
* @param {PositiveNumber} alpha - first shape parameter
* @param {PositiveNumber} beta - second shape parameter
* @returns {Probability} pseudorandom number
*/
function sample( randu, randn, alpha, beta ) {
var sigma;
var flg;
var mu;
var A;
var B;
var C;
var L;
var s;
var u;
var x;
var y;
A = alpha - 1.0;
B = beta - 1.0;
C = A + B;
L = C * ln( C );
mu = A / C;
sigma = 0.5 / pow( C, 0.5 );
flg = true;
while ( flg === true ) {
s = randn();
x = mu + (s*sigma);
if ( x >= 0.0 && x <= 1.0 ) {
u = randu();
y = A * ln( x/A );
y += B * ln((1.0-x) / B);
y += L + (0.5*s*s);
if ( y >= ln( u ) ) {
flg = false;
}
}
}
return x;
}
// EXPORTS //
module.exports = sample;
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