/*
 * Encog(tm) Core v3.2 - Java Version
 * http://www.heatonresearch.com/encog/
 * https://github.com/encog/encog-java-core

 * Copyright 2008-2013 Heaton Research, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * For more information on Heaton Research copyrights, licenses
 * and trademarks visit:
 * http://www.heatonresearch.com/copyright
 */
package syncleus.dann.math.rbf;

/**
 * Multi-dimensional gaussian function. Do not use this to implement a 1d
 * function, simply use GaussianFunction for that.
 */
public class GaussianFunction extends BasicRBF {

    /**
     * Serial id.
     */
    private static final long serialVersionUID = 1L;

    /**
     * Default constructor, used for reflection.
     */
    public GaussianFunction() {
    }

    /**
     * Construct a single-dimension Gaussian function with the specified peak,
     * centers and widths.
     *
     * @param peak   The peak for all dimensions.
     * @param center The centers for each dimension.
     * @param width  The widths for each dimension.
     */
    public GaussianFunction(final double center, final double peak,
                            final double width) {
        setCenters(new double[1]);
        getCenters()[0] = center;
        setPeak(peak);
        setWidth(width);
    }

    /**
     * Construct a multi-dimension Gaussian function with the specified peak,
     * centers and widths.
     *
     * @param peak   The peak for all dimensions.
     * @param center The centers for each dimension.
     * @param width  The widths for each dimension.
     */
    public GaussianFunction(final double peak, final double[] center,
                            final double width) {
        setCenters(center);
        setPeak(peak);
        setWidth(width);
    }

    /**
     * Create centered at zero, width 0, and peak 0.
     *
     * @param dimensions The number of dimensions.
     */
    public GaussianFunction(final int dimensions) {
        setCenters(new double[dimensions]);
        setPeak(1.0);
        setWidth(1.0);
    }

    /**
     * Calculate the result from the function.
     *
     * @param x The parameters for the function, one for each dimension.
     * @return The result of the function.
     */
    @Override
    public final double apply(final double[] x) {
        double value = 0;
        final double[] center = getCenters();
        final double width = getWidth();

        for (int i = 0; i < center.length; i++) {
            value += Math.pow(x[i] - center[i], 2) / (2.0 * width * width);
        }
        return getPeak() * Math.exp(-value);
    }

}
