ArcTangent.java

/*
 * MIT License
 *
 * Copyright (c) 2016 Federico Vera <https://github.com/dktcoding>
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package libai.common.functions;

/**
 * Function ArcTan.
 * <pre>
 * ArcTan(x)  = tan^-1(x)
 *
 * ArcTan'(x) = 1 / (x^2 + 1)
 * </pre>
 *
 * @author Federico Vera {@literal <fedevera at unc.edu.ar>}
 */
public class ArcTangent implements Function {

    private static final long serialVersionUID = 1967026062364806506L;

    private static final Function derivate = new Function() {
        @Override
        public double eval(double x) {
            return 1. / (x * x + 1.);
        }

        @Override
        public Function getDerivate() {
            String msg = "Second derivative not implemented for 'ArcTan(x)'";
            throw new UnsupportedOperationException(msg);
        }
    };

    @Override
    public double eval(double x) {
        return Math.atan(x);
    }

    @Override
    public Function getDerivate() {
        return derivate;
    }
}