BiasedRandomFloat.java

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/*
    Synthia, a data structure generator
    Copyright (C) 2019-2021 Laboratoire d'informatique formelle
    Université du Québec à Chicoutimi, Canada
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.
 
    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package ca.uqac.lif.synthia.random;
 
/**
 * Generates pseudo-random floating-point numbers in the interval [0,1],
 * but according to a probability distribution that is not uniform.
 * Concretely, a value is first picked uniformly, and is then multiplied
 * by a factor &beta; called the bias. The resulting value is then
 * replaced by 0 or 1 if it lies outside the interval. Setting
 * &beta; &lt; 1 results in a picker that favors values closer to 0, while
 * setting &beta; &gt; 1 results in a picker that favors values closer to 1.
 * 
 * @author Sylvain Hallé
 *
 */
public class BiasedRandomFloat extends RandomFloat
{
    /**
     * The bias parameter &beta;.
     */
    protected float m_beta;
    
    /**
     * Creates a new instance of the biased random float picker.
     * @param beta The bias parameter &beta;
     */
    public BiasedRandomFloat(float beta)
    {
        super();
        m_beta = beta;
    }
    
    @Override
    public Float pick()
    {
        float f = super.pick();
        float biased_f = f * m_beta;
        if (biased_f < 0)
        {
            return 0f;
        }
        if (biased_f > 1)
        {
            return 1f - 0.000001f;
        }
        return biased_f;
    }
    
    @Override
    public BiasedRandomFloat duplicate(boolean with_state)
    {
        return new BiasedRandomFloat(m_beta);
    }
}