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

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

/**
 * Powell.
 *
 * Minimum:
 * 

 *  ƒ(x*) = 0.0
 *  x* = (3, -1, 0, 1,..., 3, -1, 0, 1)
 *  for x_i in [-4, -5]
 * 
 * 
 *
 * Characteristics:
 * 

 * Only defined for 4*N dimensions
 * 
 * 
 *
 * R(-4, -5)^32
 *
 */
public class Powell extends ContinuousFunction {

    /**
     * {@inheritDoc}
     */
    @Override
    public Double f(Vector input) {
        Preconditions.checkArgument(input.size() % 4 == 0, "Powell function is only defined for 4*N dimensions");

        double sum = 0;

        for(int i = 1; i <= input.size() / 4; i++) {
            double x[] = new double[4];
            for(int j = 4; j >= 1; j--) {
                x[4 - j] = input.doubleValueOf(4 * i - j);
            }

            sum += Math.pow(x[0] + 10 * x[1], 2);
            sum += 5 * Math.pow(x[2] - x[3], 2);
            sum += Math.pow(x[1] - 2 * x[2], 4);
            sum += 10 * Math.pow(x[0] - x[3], 4);
        }

        return sum;
    }
}