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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.commons.math.optimization.fitting;
import java.io.Serializable;
import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction;
import org.apache.commons.math.analysis.UnivariateRealFunction;
import org.apache.commons.math.exception.DimensionMismatchException;
import org.apache.commons.math.exception.util.LocalizedFormats;
import org.apache.commons.math.exception.ZeroException;
import org.apache.commons.math.exception.NullArgumentException;
/**
* A Gaussian function. Specifically:
* <p>
* <tt>f(x) = a + b*exp(-((x - c)^2 / (2*d^2)))</tt>
* <p>
* Notation key:
* <ul>
* <li><tt>x^n</tt>: <tt>x</tt> raised to the power of <tt>n</tt>
* <li><tt>exp(x)</tt>: <i>e</i><tt>^x</tt>
* </ul>
* References:
* <ul>
* <li><a href="http://en.wikipedia.org/wiki/Gaussian_function">Wikipedia:
* Gaussian function</a>
* </ul>
*
* @see GaussianDerivativeFunction
* @see ParametricGaussianFunction
* @since 2.2
* @version $Revision: 1037327 $ $Date: 2010-11-20 21:57:37 +0100 (sam. 20 nov. 2010) $
*/
public class GaussianFunction implements DifferentiableUnivariateRealFunction, Serializable {
/** Serializable version identifier. */
private static final long serialVersionUID = -3195385616125629512L;
/** Parameter a of this function. */
private final double a;
/** Parameter b of this function. */
private final double b;
/** Parameter c of this function. */
private final double c;
/** Parameter d of this function. */
private final double d;
/**
* Constructs an instance with the specified parameters.
*
* @param a <tt>a</tt> parameter value
* @param b <tt>b</tt> parameter value
* @param c <tt>c</tt> parameter value
* @param d <tt>d</tt> parameter value
*
* @throws IllegalArgumentException if <code>d</code> is 0
*/
public GaussianFunction(double a, double b, double c, double d) {
if (d == 0.0) {
throw new ZeroException();
}
this.a = a;
this.b = b;
this.c = c;
this.d = d;
}
/**
* Constructs an instance with the specified parameters.
*
* @param parameters <tt>a</tt>, <tt>b</tt>, <tt>c</tt>, and <tt>d</tt>
* parameter values
*
* @throws IllegalArgumentException if <code>parameters</code> is null,
* <code>parameters</code> length is not 4, or if
* <code>parameters[3]</code> is 0
*/
public GaussianFunction(double[] parameters) {
if (parameters == null) {
throw new NullArgumentException(LocalizedFormats.INPUT_ARRAY);
}
if (parameters.length != 4) {
throw new DimensionMismatchException(4, parameters.length);
}
if (parameters[3] == 0.0) {
throw new ZeroException();
}
this.a = parameters[0];
this.b = parameters[1];
this.c = parameters[2];
this.d = parameters[3];
}
/** {@inheritDoc} */
public UnivariateRealFunction derivative() {
return new GaussianDerivativeFunction(b, c, d);
}
/** {@inheritDoc} */
public double value(double x) {
final double xMc = x - c;
return a + b * Math.exp(-xMc * xMc / (2.0 * (d * d)));
}
/**
* Gets <tt>a</tt> parameter value.
*
* @return <tt>a</tt> parameter value
*/
public double getA() {
return a;
}
/**
* Gets <tt>b</tt> parameter value.
*
* @return <tt>b</tt> parameter value
*/
public double getB() {
return b;
}
/**
* Gets <tt>c</tt> parameter value.
*
* @return <tt>c</tt> parameter value
*/
public double getC() {
return c;
}
/**
* Gets <tt>d</tt> parameter value.
*
* @return <tt>d</tt> parameter value
*/
public double getD() {
return d;
}
}
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