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A library of composable components enabling simpler Computational Intelligence

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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;

/**
 * The Salomon Function.
 *
 * Reference: R. Salomon Re-evaluating genetic algorithm performance under coordinate rotation of benchmark functions. A survey of some
 * theoretical and practical aspects of genetic algorithms,
 * Biosystems, 1996
 *
 * Minimum:
 * 

 *  ƒ(x*) = 0
 *  x* = (0, 0, ...., 0)
 *  for x_i in [-600, 600]
 * 
 * 
 * 
 * Characteristics:
 * 

 * Multimodal
 * Non-separable
 * 
 * 
 * f(x) = 0; x = (0,0,...,0); x_i e (-600,600)
 *
 * R(-600, 600)^30
 *
 */
public class Salomon implements ContinuousFunction {

    private static final long serialVersionUID = -6002240316648057218L;

    /**
     * {@inheritDoc}
     */
    @Override
    public Double apply(Vector input) {
        double sumSquares = 0.0;

        for (int i = 0; i < input.size(); i++) {
            sumSquares += input.doubleValueOf(i) * input.doubleValueOf(i);
        }

        return -(Math.cos(2 * Math.PI * Math.sqrt(sumSquares))) + (0.1 * Math.sqrt(sumSquares)) + 1;
    }
}