ingo@1115: /*
ingo@1115:  * Copyright (c) 2010 by Intevation GmbH
ingo@1115:  *
ingo@1115:  * This program is free software under the LGPL (>=v2.1)
ingo@1115:  * Read the file LGPL.txt coming with the software for details
ingo@1115:  * or visit http://www.gnu.org/licenses/ if it does not exist.
ingo@1115:  */
ingo@1115: 
sascha@357: package de.intevation.gnv.math;
sascha@357: 
sascha@357: import org.apache.commons.math.FunctionEvaluationException;
sascha@357: 
sascha@433: import org.apache.commons.math.analysis.UnivariateRealFunction;
sascha@433: 
sascha@779: import org.apache.commons.math.optimization.fitting.ParametricRealFunction;
sascha@779: 
sascha@357: /**
sascha@807:  * Models a linear function to be usable in the fitting framework of
sascha@805:  * the Apache Commons Mathematics Library.
sascha@805:  *
sascha@780:  *  @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
sascha@357:  */
sascha@357: public class LinearFunction
sascha@357: implements   ParametricRealFunction
sascha@357: {
sascha@805:     /**
sascha@805:      * Instance to prevent needless creations of instances.
sascha@805:      */
sascha@357:     public static final LinearFunction INSTANCE = new LinearFunction();
sascha@357: 
sascha@805:     /**
sascha@805:      * Specialized class to be useful in function evaluating
sascha@805:      * in the Apache Commons Mathematics Library.
sascha@805:      */
sascha@778:     public static class Univariate
sascha@433:     implements          UnivariateRealFunction
sascha@433:     {
sascha@805:         /**
sascha@805:          * The linear scaling factor.
sascha@805:          */
sascha@433:         protected double m;
sascha@805:         /**
sascha@805:          * The linear offset.
sascha@805:          */
sascha@433:         protected double b;
sascha@433: 
sascha@805:         /**
sascha@805:          * Default constructor.
sascha@805:          */
sascha@433:         public Univariate() {
sascha@433:         }
sascha@433: 
sascha@805:         /**
sascha@805:          * Constructor to create a Univariate with the linear parameters
sascha@805:          * of the line between (x1, y1) and (x2, y2).
sascha@805:          * @param x1 The x coordinate of the first point.
sascha@805:          * @param y1 The y coordinate of the first point.
sascha@805:          * @param x2 The x coordinate of the second point.
sascha@805:          * @param y2 The y coordinate of the second point.
sascha@805:          */
sascha@433:         public Univariate(double x1, double y1, double x2, double y2) {
sascha@433:             if (y1 == y2) {
sascha@433:                 m = 0d;
sascha@433:                 b = (x1 + x2)*0.5d;
sascha@433:             }
sascha@433:             else {
sascha@433:                 m = (x1 - x2)/(y1 - y2);
sascha@433:                 b = y1 - m*x1;
sascha@433:             }
sascha@433:         }
sascha@433: 
sascha@433:         public double value(double x) {
sascha@433:             return m*x + b;
sascha@433:         }
sascha@433:     } // class Univariate
sascha@433: 
sascha@805:     /**
sascha@805:      * Default constructor.
sascha@805:      */
sascha@357:     public LinearFunction() {
sascha@357:     }
sascha@357: 
sascha@357:     public double value(double x, double [] parameters)
sascha@778:     throws FunctionEvaluationException
sascha@357:     {
sascha@357:         return x*parameters[0] + parameters[1];
sascha@357:     }
sascha@357: 
sascha@778:     public double [] gradient(double x, double [] parameters)
sascha@778:     throws FunctionEvaluationException
sascha@357:     {
sascha@357:         return new double [] { x, 1f };
sascha@357:     }
sascha@357: }
sascha@514: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :