net.sourceforge.cilib.functions.continuous.unconstrained.EggHolder 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;

/**
 * The Egg Holder.
 *
 * Reference: S.K. Mishra, Some New Test Functions
 * for Global Optimization and Performance of Repulsive Particle
 * Swarm Methods, Technical Report, North-Eastern Hill University,
 * India, 2006
 *
 * Note: n >= 2
 *
 * Minimum:
 * 

 *  f(x*) approx -959.64 
 *  x* = (512,404.2319) for n=2
 *  for x_i in [-512,512]
 * 
 * 
 *
 * Characteristics:
 * 

 * Only defined for 2+ dimensions
 * Multimodal
 * Non-separable
 * Not regular
 * 
 * 
 *
 * R(-512.0,512.0)^30
 *
 */
public class EggHolder extends ContinuousFunction {

    private static final long serialVersionUID = 358993985066821115L;

    @Override
    public Double f(Vector input) {
        Preconditions.checkArgument(input.size() >= 2, "EggHolder function is only defined for 2 or more dimensions");

        double sum = 0.0;
        for (int i = 0; i < input.size() - 1; i++) {
            sum += (-1*(input.doubleValueOf(i+1) + 47)
                    *Math.sin(Math.sqrt(Math.abs(input.doubleValueOf(i+1) + input.doubleValueOf(i)/2 + 47)))
                    + Math.sin(Math.sqrt(Math.abs(input.doubleValueOf(i) - (input.doubleValueOf(i+1)+47))))
                    *(-1*input.doubleValueOf(i)));
        }
        return sum;
    }
}