/** Copyright (C) 2017 by Bundesanstalt für Gewässerkunde
 * Software engineering by
 *  Björnsen Beratende Ingenieure GmbH
 *  Dr. Schumacher Ingenieurbüro für Wasser und Umwelt
 *
 * This file is Free Software under the GNU AGPL (>=v3)
 * and comes with ABSOLUTELY NO WARRANTY! Check out the
 * documentation coming with Dive4Elements River for details.
 */
package org.dive4elements.river.artifacts.math.fitting;

/**
 * @author Domenico Nardi Tironi
 *
 */
/*
 * Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
 * Software engineering by Intevation GmbH
 * This file is Free Software under the GNU AGPL (>=v3)
 * and comes with ABSOLUTELY NO WARRANTY! Check out the
 * documentation coming with Dive4Elements River for details.
 */

public abstract class AbstractLogLinear extends Function {
    public static final Derivative DERIVATIVE = new Derivative("W'(Q) = a*m/(m*Q + b)") {

        @Override
        public org.dive4elements.river.artifacts.math.Function instantiate(final double[] parameters) {
            final double a = parameters[0];
            final double m = parameters[1];
            final double b = parameters[2];

            return new org.dive4elements.river.artifacts.math.Function() {
                @Override
                public double value(final double Q) {
                    return a * m / (m * Q + b);
                }
            };
        }
    };

    public AbstractLogLinear(final String name, final String description) {
        super(name, description, new String[] { "a", "m", "b" });
    }

    @Override
    public final double value(final double x, final double[] parameters) {
        return parameters[0] * Math.log(parameters[1] * x + parameters[2]);
    }

    @Override
    public double[] gradient(final double x, final double[] parameters) {
        final double a = parameters[0];
        final double m = parameters[1];
        final double b = parameters[2];

        final double lin = m * x + b;

        return new double[] { Math.log(lin), a * x / lin, a / lin };
    }

    @Override
    public final Derivative getDerivative() {
        return DERIVATIVE;
    }

    @Override
    public Function getInverse() {
        return InvLogLinear.INSTANCE;
    }
}
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