net.sourceforge.cilib.functions.continuous.unconstrained.Spherical 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.functions.Differentiable;
import net.sourceforge.cilib.type.types.Numeric;
import net.sourceforge.cilib.type.types.Real;
import net.sourceforge.cilib.type.types.container.Vector;
import fj.F;

/**
 * Spherical function.
 *
 * Reference: X. Yao, Y. Liu, G. Liu, Evolutionary Programming
 * Made Faster,  IEEE Transactions on Evolutionary Computation,
 * 3(2):82--102, 1999
 *
 * 
 * Characteristics:
 * 

 * Unimodal
 * Continuous
 * Separable
 * Regular
 * Convex
 * 
 * 
 *
 * f(x) = 0; x = (0,0,...,0)
 * x e [-5.12, 5.12]
 *
 * R(-5.12, 5.12)^30
 *
 */
public class Spherical extends ContinuousFunction implements Differentiable {

    private static final long serialVersionUID = 5811377575647995206L;

    /**
     * {@inheritDoc}
     */
    @Override
    public Double f(Vector input) {
        return input.foldLeft(0.0, new F() {
            @Override
            public Double f(Numeric x) {
                return x.doubleValue() * x.doubleValue();
            }
        });
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Vector getGradient(Vector x) {
        return x.map(new F() {
            @Override
            public Numeric f(Numeric x) {
                return Real.valueOf(x.doubleValue() * 2);
            }
        });
    }
}