Mercurial > hg > de.mpg.mpiwg.itgroup.digilib.plugin
view libs/commons-math-2.1/docs/apidocs/src-html/org/apache/commons/math/ode/FirstOrderConverter.html @ 13:cbf34dd4d7e6
commons-math-2.1 added
| author | dwinter |
|---|---|
| date | Tue, 04 Jan 2011 10:02:07 +0100 |
| parents | |
| children |
line wrap: on
line source
<HTML> <BODY BGCOLOR="white"> <PRE> <FONT color="green">001</FONT> /*<a name="line.1"></a> <FONT color="green">002</FONT> * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a> <FONT color="green">003</FONT> * contributor license agreements. See the NOTICE file distributed with<a name="line.3"></a> <FONT color="green">004</FONT> * this work for additional information regarding copyright ownership.<a name="line.4"></a> <FONT color="green">005</FONT> * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a> <FONT color="green">006</FONT> * (the "License"); you may not use this file except in compliance with<a name="line.6"></a> <FONT color="green">007</FONT> * the License. You may obtain a copy of the License at<a name="line.7"></a> <FONT color="green">008</FONT> *<a name="line.8"></a> <FONT color="green">009</FONT> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a> <FONT color="green">010</FONT> *<a name="line.10"></a> <FONT color="green">011</FONT> * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a> <FONT color="green">012</FONT> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a> <FONT color="green">013</FONT> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a> <FONT color="green">014</FONT> * See the License for the specific language governing permissions and<a name="line.14"></a> <FONT color="green">015</FONT> * limitations under the License.<a name="line.15"></a> <FONT color="green">016</FONT> */<a name="line.16"></a> <FONT color="green">017</FONT> <a name="line.17"></a> <FONT color="green">018</FONT> package org.apache.commons.math.ode;<a name="line.18"></a> <FONT color="green">019</FONT> <a name="line.19"></a> <FONT color="green">020</FONT> /** This class converts second order differential equations to first<a name="line.20"></a> <FONT color="green">021</FONT> * order ones.<a name="line.21"></a> <FONT color="green">022</FONT> *<a name="line.22"></a> <FONT color="green">023</FONT> * <p>This class is a wrapper around a {@link<a name="line.23"></a> <FONT color="green">024</FONT> * SecondOrderDifferentialEquations} which allow to use a {@link<a name="line.24"></a> <FONT color="green">025</FONT> * FirstOrderIntegrator} to integrate it.</p><a name="line.25"></a> <FONT color="green">026</FONT> *<a name="line.26"></a> <FONT color="green">027</FONT> * <p>The transformation is done by changing the n dimension state<a name="line.27"></a> <FONT color="green">028</FONT> * vector to a 2n dimension vector, where the first n components are<a name="line.28"></a> <FONT color="green">029</FONT> * the initial state variables and the n last components are their<a name="line.29"></a> <FONT color="green">030</FONT> * first time derivative. The first time derivative of this state<a name="line.30"></a> <FONT color="green">031</FONT> * vector then really contains both the first and second time<a name="line.31"></a> <FONT color="green">032</FONT> * derivative of the initial state vector, which can be handled by the<a name="line.32"></a> <FONT color="green">033</FONT> * underlying second order equations set.</p><a name="line.33"></a> <FONT color="green">034</FONT> *<a name="line.34"></a> <FONT color="green">035</FONT> * <p>One should be aware that the data is duplicated during the<a name="line.35"></a> <FONT color="green">036</FONT> * transformation process and that for each call to {@link<a name="line.36"></a> <FONT color="green">037</FONT> * #computeDerivatives computeDerivatives}, this wrapper does copy 4n<a name="line.37"></a> <FONT color="green">038</FONT> * scalars : 2n before the call to {@link<a name="line.38"></a> <FONT color="green">039</FONT> * SecondOrderDifferentialEquations#computeSecondDerivatives<a name="line.39"></a> <FONT color="green">040</FONT> * computeSecondDerivatives} in order to dispatch the y state vector<a name="line.40"></a> <FONT color="green">041</FONT> * into z and zDot, and 2n after the call to gather zDot and zDDot<a name="line.41"></a> <FONT color="green">042</FONT> * into yDot. Since the underlying problem by itself perhaps also<a name="line.42"></a> <FONT color="green">043</FONT> * needs to copy data and dispatch the arrays into domain objects,<a name="line.43"></a> <FONT color="green">044</FONT> * this has an impact on both memory and CPU usage. The only way to<a name="line.44"></a> <FONT color="green">045</FONT> * avoid this duplication is to perform the transformation at the<a name="line.45"></a> <FONT color="green">046</FONT> * problem level, i.e. to implement the problem as a first order one<a name="line.46"></a> <FONT color="green">047</FONT> * and then avoid using this class.</p><a name="line.47"></a> <FONT color="green">048</FONT> *<a name="line.48"></a> <FONT color="green">049</FONT> * @see FirstOrderIntegrator<a name="line.49"></a> <FONT color="green">050</FONT> * @see FirstOrderDifferentialEquations<a name="line.50"></a> <FONT color="green">051</FONT> * @see SecondOrderDifferentialEquations<a name="line.51"></a> <FONT color="green">052</FONT> * @version $Revision: 811827 $ $Date: 2009-09-06 11:32:50 -0400 (Sun, 06 Sep 2009) $<a name="line.52"></a> <FONT color="green">053</FONT> * @since 1.2<a name="line.53"></a> <FONT color="green">054</FONT> */<a name="line.54"></a> <FONT color="green">055</FONT> <a name="line.55"></a> <FONT color="green">056</FONT> public class FirstOrderConverter implements FirstOrderDifferentialEquations {<a name="line.56"></a> <FONT color="green">057</FONT> <a name="line.57"></a> <FONT color="green">058</FONT> /** Underlying second order equations set. */<a name="line.58"></a> <FONT color="green">059</FONT> private final SecondOrderDifferentialEquations equations;<a name="line.59"></a> <FONT color="green">060</FONT> <a name="line.60"></a> <FONT color="green">061</FONT> /** second order problem dimension. */<a name="line.61"></a> <FONT color="green">062</FONT> private final int dimension;<a name="line.62"></a> <FONT color="green">063</FONT> <a name="line.63"></a> <FONT color="green">064</FONT> /** state vector. */<a name="line.64"></a> <FONT color="green">065</FONT> private final double[] z;<a name="line.65"></a> <FONT color="green">066</FONT> <a name="line.66"></a> <FONT color="green">067</FONT> /** first time derivative of the state vector. */<a name="line.67"></a> <FONT color="green">068</FONT> private final double[] zDot;<a name="line.68"></a> <FONT color="green">069</FONT> <a name="line.69"></a> <FONT color="green">070</FONT> /** second time derivative of the state vector. */<a name="line.70"></a> <FONT color="green">071</FONT> private final double[] zDDot;<a name="line.71"></a> <FONT color="green">072</FONT> <a name="line.72"></a> <FONT color="green">073</FONT> /** Simple constructor.<a name="line.73"></a> <FONT color="green">074</FONT> * Build a converter around a second order equations set.<a name="line.74"></a> <FONT color="green">075</FONT> * @param equations second order equations set to convert<a name="line.75"></a> <FONT color="green">076</FONT> */<a name="line.76"></a> <FONT color="green">077</FONT> public FirstOrderConverter (final SecondOrderDifferentialEquations equations) {<a name="line.77"></a> <FONT color="green">078</FONT> this.equations = equations;<a name="line.78"></a> <FONT color="green">079</FONT> dimension = equations.getDimension();<a name="line.79"></a> <FONT color="green">080</FONT> z = new double[dimension];<a name="line.80"></a> <FONT color="green">081</FONT> zDot = new double[dimension];<a name="line.81"></a> <FONT color="green">082</FONT> zDDot = new double[dimension];<a name="line.82"></a> <FONT color="green">083</FONT> }<a name="line.83"></a> <FONT color="green">084</FONT> <a name="line.84"></a> <FONT color="green">085</FONT> /** Get the dimension of the problem.<a name="line.85"></a> <FONT color="green">086</FONT> * <p>The dimension of the first order problem is twice the<a name="line.86"></a> <FONT color="green">087</FONT> * dimension of the underlying second order problem.</p><a name="line.87"></a> <FONT color="green">088</FONT> * @return dimension of the problem<a name="line.88"></a> <FONT color="green">089</FONT> */<a name="line.89"></a> <FONT color="green">090</FONT> public int getDimension() {<a name="line.90"></a> <FONT color="green">091</FONT> return 2 * dimension;<a name="line.91"></a> <FONT color="green">092</FONT> }<a name="line.92"></a> <FONT color="green">093</FONT> <a name="line.93"></a> <FONT color="green">094</FONT> /** Get the current time derivative of the state vector.<a name="line.94"></a> <FONT color="green">095</FONT> * @param t current value of the independent <I>time</I> variable<a name="line.95"></a> <FONT color="green">096</FONT> * @param y array containing the current value of the state vector<a name="line.96"></a> <FONT color="green">097</FONT> * @param yDot placeholder array where to put the time derivative of the state vector<a name="line.97"></a> <FONT color="green">098</FONT> * @throws DerivativeException this exception is propagated to the caller if the<a name="line.98"></a> <FONT color="green">099</FONT> * underlying user function triggers one<a name="line.99"></a> <FONT color="green">100</FONT> */<a name="line.100"></a> <FONT color="green">101</FONT> public void computeDerivatives(final double t, final double[] y, final double[] yDot)<a name="line.101"></a> <FONT color="green">102</FONT> throws DerivativeException {<a name="line.102"></a> <FONT color="green">103</FONT> <a name="line.103"></a> <FONT color="green">104</FONT> // split the state vector in two<a name="line.104"></a> <FONT color="green">105</FONT> System.arraycopy(y, 0, z, 0, dimension);<a name="line.105"></a> <FONT color="green">106</FONT> System.arraycopy(y, dimension, zDot, 0, dimension);<a name="line.106"></a> <FONT color="green">107</FONT> <a name="line.107"></a> <FONT color="green">108</FONT> // apply the underlying equations set<a name="line.108"></a> <FONT color="green">109</FONT> equations.computeSecondDerivatives(t, z, zDot, zDDot);<a name="line.109"></a> <FONT color="green">110</FONT> <a name="line.110"></a> <FONT color="green">111</FONT> // build the result state derivative<a name="line.111"></a> <FONT color="green">112</FONT> System.arraycopy(zDot, 0, yDot, 0, dimension);<a name="line.112"></a> <FONT color="green">113</FONT> System.arraycopy(zDDot, 0, yDot, dimension, dimension);<a name="line.113"></a> <FONT color="green">114</FONT> <a name="line.114"></a> <FONT color="green">115</FONT> }<a name="line.115"></a> <FONT color="green">116</FONT> <a name="line.116"></a> <FONT color="green">117</FONT> }<a name="line.117"></a> </PRE> </BODY> </HTML>