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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 standardGamma = require( './standard_gamma.js' );
var sample1 = require( './sample1.js' );
var sample2 = require( './sample2.js' );
var sample3 = require( './sample3.js' );
// MAIN //
/**
* Returns a random number drawn from a beta distribution.
*
* @private
* @param {PRNG} randu - pseudorandom number generator for uniformly distributed numbers
* @param {PRNG} randn - pseudorandom number generator 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 ga;
var gb;
if ( alpha === beta && alpha > 1.5 ) {
return sample1( randu, randn, alpha );
}
if ( alpha > 1.0 && beta > 1.0 ) {
return sample2( randu, randn, alpha, beta );
}
if ( alpha < 1.0 && beta < 1.0 ) {
return sample3( randu, alpha, beta );
}
// General case of using two gamma random variates:
ga = standardGamma( randu, randn, alpha );
gb = standardGamma( randu, randn, beta );
return ga / ( ga + gb );
}
// EXPORTS //
module.exports = sample;
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