net.sourceforge.cilib.functions.continuous.unconstrained.Branin Maven / Gradle / Ivy

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/**           __  __
 *    _____ _/ /_/ /_    Computational Intelligence Library (CIlib)
 *   / ___/ / / / __ \   (c) CIRG @ UP
 *  / /__/ / / / /_/ /   http://cilib.net
 *  \___/_/_/_/_.___/
 */
package net.sourceforge.cilib.functions.continuous.unconstrained;

import net.sourceforge.cilib.functions.ContinuousFunction;
import net.sourceforge.cilib.type.types.container.Vector;

import com.google.common.base.Preconditions;

/**
 * Branin Function
 *
 * Reference: X. Yao, Y. Liu, G. Liu, Evolutionary Programming Made Faster,
 * IEEE Transactions on Evolutionary Computation, 3(1):82--102, 1999
 *
 * Minimum:
 * 

 *  ƒ(x*) = 0.397887 
 *  x* = (-π, 12.275), (π, 2.275), (9.425, 2.425)
 *  for x₁ in [-5,10], x₂ in [0,15]
 * 
 * 
 *
 * Characteristics:
 * 

 * Only defined for 2 dimensions
 * Has 3 global minima
 * Unimodal
 * Seperable
 * Regular
 * 
 * 
 *
 * R(-5,10),R(0,15)
 *
 *
 */
public class Branin extends ContinuousFunction {

    private static final long serialVersionUID = -2254223453957430344L;
    private double a = 1.0;
    private double b = 5.1 / (4 * Math.PI * Math.PI);
    private double c = 5.0 / Math.PI;
    private double d = 6.0;
    private double e = 10.0;
    private double f = 1.0 / (8.0 * Math.PI);

    /**
     * Create a new instance of {@linkplain Branin}. Domain defaults to: R(-5,10),R(0,15)
     */
    public Branin() {
        a = 1.0;
        b = 5.1 / (4 * Math.PI * Math.PI);
        c = 5.0 / Math.PI;
        d = 6.0;
        e = 10.0;
        f = 1.0 / (8.0 * Math.PI);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Double f(Vector input) {
        Preconditions.checkArgument(input.size() == 2, "Branin function is only defined for 2 dimensions");

        double x1 = input.doubleValueOf(0);
        double x2 = input.doubleValueOf(1);

        return a * Math.pow((x2 - b * x1 * x1 + c * x1 - d), 2) + e * (1 - f) * Math.cos(x1) + e;
    }
}