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| date | Tue, 04 Jan 2011 10:02:07 +0100 |
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<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.nonstiff;<a name="line.18"></a> <FONT color="green">019</FONT> <a name="line.19"></a> <FONT color="green">020</FONT> import org.apache.commons.math.ode.DerivativeException;<a name="line.20"></a> <FONT color="green">021</FONT> import org.apache.commons.math.ode.FirstOrderDifferentialEquations;<a name="line.21"></a> <FONT color="green">022</FONT> import org.apache.commons.math.ode.IntegratorException;<a name="line.22"></a> <FONT color="green">023</FONT> import org.apache.commons.math.ode.events.CombinedEventsManager;<a name="line.23"></a> <FONT color="green">024</FONT> import org.apache.commons.math.ode.sampling.AbstractStepInterpolator;<a name="line.24"></a> <FONT color="green">025</FONT> import org.apache.commons.math.ode.sampling.DummyStepInterpolator;<a name="line.25"></a> <FONT color="green">026</FONT> import org.apache.commons.math.ode.sampling.StepHandler;<a name="line.26"></a> <FONT color="green">027</FONT> <a name="line.27"></a> <FONT color="green">028</FONT> /**<a name="line.28"></a> <FONT color="green">029</FONT> * This class implements the common part of all embedded Runge-Kutta<a name="line.29"></a> <FONT color="green">030</FONT> * integrators for Ordinary Differential Equations.<a name="line.30"></a> <FONT color="green">031</FONT> *<a name="line.31"></a> <FONT color="green">032</FONT> * <p>These methods are embedded explicit Runge-Kutta methods with two<a name="line.32"></a> <FONT color="green">033</FONT> * sets of coefficients allowing to estimate the error, their Butcher<a name="line.33"></a> <FONT color="green">034</FONT> * arrays are as follows :<a name="line.34"></a> <FONT color="green">035</FONT> * <pre><a name="line.35"></a> <FONT color="green">036</FONT> * 0 |<a name="line.36"></a> <FONT color="green">037</FONT> * c2 | a21<a name="line.37"></a> <FONT color="green">038</FONT> * c3 | a31 a32<a name="line.38"></a> <FONT color="green">039</FONT> * ... | ...<a name="line.39"></a> <FONT color="green">040</FONT> * cs | as1 as2 ... ass-1<a name="line.40"></a> <FONT color="green">041</FONT> * |--------------------------<a name="line.41"></a> <FONT color="green">042</FONT> * | b1 b2 ... bs-1 bs<a name="line.42"></a> <FONT color="green">043</FONT> * | b'1 b'2 ... b's-1 b's<a name="line.43"></a> <FONT color="green">044</FONT> * </pre><a name="line.44"></a> <FONT color="green">045</FONT> * </p><a name="line.45"></a> <FONT color="green">046</FONT> *<a name="line.46"></a> <FONT color="green">047</FONT> * <p>In fact, we rather use the array defined by ej = bj - b'j to<a name="line.47"></a> <FONT color="green">048</FONT> * compute directly the error rather than computing two estimates and<a name="line.48"></a> <FONT color="green">049</FONT> * then comparing them.</p><a name="line.49"></a> <FONT color="green">050</FONT> *<a name="line.50"></a> <FONT color="green">051</FONT> * <p>Some methods are qualified as <i>fsal</i> (first same as last)<a name="line.51"></a> <FONT color="green">052</FONT> * methods. This means the last evaluation of the derivatives in one<a name="line.52"></a> <FONT color="green">053</FONT> * step is the same as the first in the next step. Then, this<a name="line.53"></a> <FONT color="green">054</FONT> * evaluation can be reused from one step to the next one and the cost<a name="line.54"></a> <FONT color="green">055</FONT> * of such a method is really s-1 evaluations despite the method still<a name="line.55"></a> <FONT color="green">056</FONT> * has s stages. This behaviour is true only for successful steps, if<a name="line.56"></a> <FONT color="green">057</FONT> * the step is rejected after the error estimation phase, no<a name="line.57"></a> <FONT color="green">058</FONT> * evaluation is saved. For an <i>fsal</i> method, we have cs = 1 and<a name="line.58"></a> <FONT color="green">059</FONT> * asi = bi for all i.</p><a name="line.59"></a> <FONT color="green">060</FONT> *<a name="line.60"></a> <FONT color="green">061</FONT> * @version $Revision: 927202 $ $Date: 2010-03-24 18:11:51 -0400 (Wed, 24 Mar 2010) $<a name="line.61"></a> <FONT color="green">062</FONT> * @since 1.2<a name="line.62"></a> <FONT color="green">063</FONT> */<a name="line.63"></a> <FONT color="green">064</FONT> <a name="line.64"></a> <FONT color="green">065</FONT> public abstract class EmbeddedRungeKuttaIntegrator<a name="line.65"></a> <FONT color="green">066</FONT> extends AdaptiveStepsizeIntegrator {<a name="line.66"></a> <FONT color="green">067</FONT> <a name="line.67"></a> <FONT color="green">068</FONT> /** Indicator for <i>fsal</i> methods. */<a name="line.68"></a> <FONT color="green">069</FONT> private final boolean fsal;<a name="line.69"></a> <FONT color="green">070</FONT> <a name="line.70"></a> <FONT color="green">071</FONT> /** Time steps from Butcher array (without the first zero). */<a name="line.71"></a> <FONT color="green">072</FONT> private final double[] c;<a name="line.72"></a> <FONT color="green">073</FONT> <a name="line.73"></a> <FONT color="green">074</FONT> /** Internal weights from Butcher array (without the first empty row). */<a name="line.74"></a> <FONT color="green">075</FONT> private final double[][] a;<a name="line.75"></a> <FONT color="green">076</FONT> <a name="line.76"></a> <FONT color="green">077</FONT> /** External weights for the high order method from Butcher array. */<a name="line.77"></a> <FONT color="green">078</FONT> private final double[] b;<a name="line.78"></a> <FONT color="green">079</FONT> <a name="line.79"></a> <FONT color="green">080</FONT> /** Prototype of the step interpolator. */<a name="line.80"></a> <FONT color="green">081</FONT> private final RungeKuttaStepInterpolator prototype;<a name="line.81"></a> <FONT color="green">082</FONT> <a name="line.82"></a> <FONT color="green">083</FONT> /** Stepsize control exponent. */<a name="line.83"></a> <FONT color="green">084</FONT> private final double exp;<a name="line.84"></a> <FONT color="green">085</FONT> <a name="line.85"></a> <FONT color="green">086</FONT> /** Safety factor for stepsize control. */<a name="line.86"></a> <FONT color="green">087</FONT> private double safety;<a name="line.87"></a> <FONT color="green">088</FONT> <a name="line.88"></a> <FONT color="green">089</FONT> /** Minimal reduction factor for stepsize control. */<a name="line.89"></a> <FONT color="green">090</FONT> private double minReduction;<a name="line.90"></a> <FONT color="green">091</FONT> <a name="line.91"></a> <FONT color="green">092</FONT> /** Maximal growth factor for stepsize control. */<a name="line.92"></a> <FONT color="green">093</FONT> private double maxGrowth;<a name="line.93"></a> <FONT color="green">094</FONT> <a name="line.94"></a> <FONT color="green">095</FONT> /** Build a Runge-Kutta integrator with the given Butcher array.<a name="line.95"></a> <FONT color="green">096</FONT> * @param name name of the method<a name="line.96"></a> <FONT color="green">097</FONT> * @param fsal indicate that the method is an <i>fsal</i><a name="line.97"></a> <FONT color="green">098</FONT> * @param c time steps from Butcher array (without the first zero)<a name="line.98"></a> <FONT color="green">099</FONT> * @param a internal weights from Butcher array (without the first empty row)<a name="line.99"></a> <FONT color="green">100</FONT> * @param b propagation weights for the high order method from Butcher array<a name="line.100"></a> <FONT color="green">101</FONT> * @param prototype prototype of the step interpolator to use<a name="line.101"></a> <FONT color="green">102</FONT> * @param minStep minimal step (must be positive even for backward<a name="line.102"></a> <FONT color="green">103</FONT> * integration), the last step can be smaller than this<a name="line.103"></a> <FONT color="green">104</FONT> * @param maxStep maximal step (must be positive even for backward<a name="line.104"></a> <FONT color="green">105</FONT> * integration)<a name="line.105"></a> <FONT color="green">106</FONT> * @param scalAbsoluteTolerance allowed absolute error<a name="line.106"></a> <FONT color="green">107</FONT> * @param scalRelativeTolerance allowed relative error<a name="line.107"></a> <FONT color="green">108</FONT> */<a name="line.108"></a> <FONT color="green">109</FONT> protected EmbeddedRungeKuttaIntegrator(final String name, final boolean fsal,<a name="line.109"></a> <FONT color="green">110</FONT> final double[] c, final double[][] a, final double[] b,<a name="line.110"></a> <FONT color="green">111</FONT> final RungeKuttaStepInterpolator prototype,<a name="line.111"></a> <FONT color="green">112</FONT> final double minStep, final double maxStep,<a name="line.112"></a> <FONT color="green">113</FONT> final double scalAbsoluteTolerance,<a name="line.113"></a> <FONT color="green">114</FONT> final double scalRelativeTolerance) {<a name="line.114"></a> <FONT color="green">115</FONT> <a name="line.115"></a> <FONT color="green">116</FONT> super(name, minStep, maxStep, scalAbsoluteTolerance, scalRelativeTolerance);<a name="line.116"></a> <FONT color="green">117</FONT> <a name="line.117"></a> <FONT color="green">118</FONT> this.fsal = fsal;<a name="line.118"></a> <FONT color="green">119</FONT> this.c = c;<a name="line.119"></a> <FONT color="green">120</FONT> this.a = a;<a name="line.120"></a> <FONT color="green">121</FONT> this.b = b;<a name="line.121"></a> <FONT color="green">122</FONT> this.prototype = prototype;<a name="line.122"></a> <FONT color="green">123</FONT> <a name="line.123"></a> <FONT color="green">124</FONT> exp = -1.0 / getOrder();<a name="line.124"></a> <FONT color="green">125</FONT> <a name="line.125"></a> <FONT color="green">126</FONT> // set the default values of the algorithm control parameters<a name="line.126"></a> <FONT color="green">127</FONT> setSafety(0.9);<a name="line.127"></a> <FONT color="green">128</FONT> setMinReduction(0.2);<a name="line.128"></a> <FONT color="green">129</FONT> setMaxGrowth(10.0);<a name="line.129"></a> <FONT color="green">130</FONT> <a name="line.130"></a> <FONT color="green">131</FONT> }<a name="line.131"></a> <FONT color="green">132</FONT> <a name="line.132"></a> <FONT color="green">133</FONT> /** Build a Runge-Kutta integrator with the given Butcher array.<a name="line.133"></a> <FONT color="green">134</FONT> * @param name name of the method<a name="line.134"></a> <FONT color="green">135</FONT> * @param fsal indicate that the method is an <i>fsal</i><a name="line.135"></a> <FONT color="green">136</FONT> * @param c time steps from Butcher array (without the first zero)<a name="line.136"></a> <FONT color="green">137</FONT> * @param a internal weights from Butcher array (without the first empty row)<a name="line.137"></a> <FONT color="green">138</FONT> * @param b propagation weights for the high order method from Butcher array<a name="line.138"></a> <FONT color="green">139</FONT> * @param prototype prototype of the step interpolator to use<a name="line.139"></a> <FONT color="green">140</FONT> * @param minStep minimal step (must be positive even for backward<a name="line.140"></a> <FONT color="green">141</FONT> * integration), the last step can be smaller than this<a name="line.141"></a> <FONT color="green">142</FONT> * @param maxStep maximal step (must be positive even for backward<a name="line.142"></a> <FONT color="green">143</FONT> * integration)<a name="line.143"></a> <FONT color="green">144</FONT> * @param vecAbsoluteTolerance allowed absolute error<a name="line.144"></a> <FONT color="green">145</FONT> * @param vecRelativeTolerance allowed relative error<a name="line.145"></a> <FONT color="green">146</FONT> */<a name="line.146"></a> <FONT color="green">147</FONT> protected EmbeddedRungeKuttaIntegrator(final String name, final boolean fsal,<a name="line.147"></a> <FONT color="green">148</FONT> final double[] c, final double[][] a, final double[] b,<a name="line.148"></a> <FONT color="green">149</FONT> final RungeKuttaStepInterpolator prototype,<a name="line.149"></a> <FONT color="green">150</FONT> final double minStep, final double maxStep,<a name="line.150"></a> <FONT color="green">151</FONT> final double[] vecAbsoluteTolerance,<a name="line.151"></a> <FONT color="green">152</FONT> final double[] vecRelativeTolerance) {<a name="line.152"></a> <FONT color="green">153</FONT> <a name="line.153"></a> <FONT color="green">154</FONT> super(name, minStep, maxStep, vecAbsoluteTolerance, vecRelativeTolerance);<a name="line.154"></a> <FONT color="green">155</FONT> <a name="line.155"></a> <FONT color="green">156</FONT> this.fsal = fsal;<a name="line.156"></a> <FONT color="green">157</FONT> this.c = c;<a name="line.157"></a> <FONT color="green">158</FONT> this.a = a;<a name="line.158"></a> <FONT color="green">159</FONT> this.b = b;<a name="line.159"></a> <FONT color="green">160</FONT> this.prototype = prototype;<a name="line.160"></a> <FONT color="green">161</FONT> <a name="line.161"></a> <FONT color="green">162</FONT> exp = -1.0 / getOrder();<a name="line.162"></a> <FONT color="green">163</FONT> <a name="line.163"></a> <FONT color="green">164</FONT> // set the default values of the algorithm control parameters<a name="line.164"></a> <FONT color="green">165</FONT> setSafety(0.9);<a name="line.165"></a> <FONT color="green">166</FONT> setMinReduction(0.2);<a name="line.166"></a> <FONT color="green">167</FONT> setMaxGrowth(10.0);<a name="line.167"></a> <FONT color="green">168</FONT> <a name="line.168"></a> <FONT color="green">169</FONT> }<a name="line.169"></a> <FONT color="green">170</FONT> <a name="line.170"></a> <FONT color="green">171</FONT> /** Get the order of the method.<a name="line.171"></a> <FONT color="green">172</FONT> * @return order of the method<a name="line.172"></a> <FONT color="green">173</FONT> */<a name="line.173"></a> <FONT color="green">174</FONT> public abstract int getOrder();<a name="line.174"></a> <FONT color="green">175</FONT> <a name="line.175"></a> <FONT color="green">176</FONT> /** Get the safety factor for stepsize control.<a name="line.176"></a> <FONT color="green">177</FONT> * @return safety factor<a name="line.177"></a> <FONT color="green">178</FONT> */<a name="line.178"></a> <FONT color="green">179</FONT> public double getSafety() {<a name="line.179"></a> <FONT color="green">180</FONT> return safety;<a name="line.180"></a> <FONT color="green">181</FONT> }<a name="line.181"></a> <FONT color="green">182</FONT> <a name="line.182"></a> <FONT color="green">183</FONT> /** Set the safety factor for stepsize control.<a name="line.183"></a> <FONT color="green">184</FONT> * @param safety safety factor<a name="line.184"></a> <FONT color="green">185</FONT> */<a name="line.185"></a> <FONT color="green">186</FONT> public void setSafety(final double safety) {<a name="line.186"></a> <FONT color="green">187</FONT> this.safety = safety;<a name="line.187"></a> <FONT color="green">188</FONT> }<a name="line.188"></a> <FONT color="green">189</FONT> <a name="line.189"></a> <FONT color="green">190</FONT> /** {@inheritDoc} */<a name="line.190"></a> <FONT color="green">191</FONT> @Override<a name="line.191"></a> <FONT color="green">192</FONT> public double integrate(final FirstOrderDifferentialEquations equations,<a name="line.192"></a> <FONT color="green">193</FONT> final double t0, final double[] y0,<a name="line.193"></a> <FONT color="green">194</FONT> final double t, final double[] y)<a name="line.194"></a> <FONT color="green">195</FONT> throws DerivativeException, IntegratorException {<a name="line.195"></a> <FONT color="green">196</FONT> <a name="line.196"></a> <FONT color="green">197</FONT> sanityChecks(equations, t0, y0, t, y);<a name="line.197"></a> <FONT color="green">198</FONT> setEquations(equations);<a name="line.198"></a> <FONT color="green">199</FONT> resetEvaluations();<a name="line.199"></a> <FONT color="green">200</FONT> final boolean forward = t > t0;<a name="line.200"></a> <FONT color="green">201</FONT> <a name="line.201"></a> <FONT color="green">202</FONT> // create some internal working arrays<a name="line.202"></a> <FONT color="green">203</FONT> final int stages = c.length + 1;<a name="line.203"></a> <FONT color="green">204</FONT> if (y != y0) {<a name="line.204"></a> <FONT color="green">205</FONT> System.arraycopy(y0, 0, y, 0, y0.length);<a name="line.205"></a> <FONT color="green">206</FONT> }<a name="line.206"></a> <FONT color="green">207</FONT> final double[][] yDotK = new double[stages][y0.length];<a name="line.207"></a> <FONT color="green">208</FONT> final double[] yTmp = new double[y0.length];<a name="line.208"></a> <FONT color="green">209</FONT> <a name="line.209"></a> <FONT color="green">210</FONT> // set up an interpolator sharing the integrator arrays<a name="line.210"></a> <FONT color="green">211</FONT> AbstractStepInterpolator interpolator;<a name="line.211"></a> <FONT color="green">212</FONT> if (requiresDenseOutput() || (! eventsHandlersManager.isEmpty())) {<a name="line.212"></a> <FONT color="green">213</FONT> final RungeKuttaStepInterpolator rki = (RungeKuttaStepInterpolator) prototype.copy();<a name="line.213"></a> <FONT color="green">214</FONT> rki.reinitialize(this, yTmp, yDotK, forward);<a name="line.214"></a> <FONT color="green">215</FONT> interpolator = rki;<a name="line.215"></a> <FONT color="green">216</FONT> } else {<a name="line.216"></a> <FONT color="green">217</FONT> interpolator = new DummyStepInterpolator(yTmp, yDotK[stages - 1], forward);<a name="line.217"></a> <FONT color="green">218</FONT> }<a name="line.218"></a> <FONT color="green">219</FONT> interpolator.storeTime(t0);<a name="line.219"></a> <FONT color="green">220</FONT> <a name="line.220"></a> <FONT color="green">221</FONT> // set up integration control objects<a name="line.221"></a> <FONT color="green">222</FONT> stepStart = t0;<a name="line.222"></a> <FONT color="green">223</FONT> double hNew = 0;<a name="line.223"></a> <FONT color="green">224</FONT> boolean firstTime = true;<a name="line.224"></a> <FONT color="green">225</FONT> for (StepHandler handler : stepHandlers) {<a name="line.225"></a> <FONT color="green">226</FONT> handler.reset();<a name="line.226"></a> <FONT color="green">227</FONT> }<a name="line.227"></a> <FONT color="green">228</FONT> CombinedEventsManager manager = addEndTimeChecker(t0, t, eventsHandlersManager);<a name="line.228"></a> <FONT color="green">229</FONT> boolean lastStep = false;<a name="line.229"></a> <FONT color="green">230</FONT> <a name="line.230"></a> <FONT color="green">231</FONT> // main integration loop<a name="line.231"></a> <FONT color="green">232</FONT> while (!lastStep) {<a name="line.232"></a> <FONT color="green">233</FONT> <a name="line.233"></a> <FONT color="green">234</FONT> interpolator.shift();<a name="line.234"></a> <FONT color="green">235</FONT> <a name="line.235"></a> <FONT color="green">236</FONT> double error = 0;<a name="line.236"></a> <FONT color="green">237</FONT> for (boolean loop = true; loop;) {<a name="line.237"></a> <FONT color="green">238</FONT> <a name="line.238"></a> <FONT color="green">239</FONT> if (firstTime || !fsal) {<a name="line.239"></a> <FONT color="green">240</FONT> // first stage<a name="line.240"></a> <FONT color="green">241</FONT> computeDerivatives(stepStart, y, yDotK[0]);<a name="line.241"></a> <FONT color="green">242</FONT> }<a name="line.242"></a> <FONT color="green">243</FONT> <a name="line.243"></a> <FONT color="green">244</FONT> if (firstTime) {<a name="line.244"></a> <FONT color="green">245</FONT> final double[] scale = new double[y0.length];<a name="line.245"></a> <FONT color="green">246</FONT> if (vecAbsoluteTolerance == null) {<a name="line.246"></a> <FONT color="green">247</FONT> for (int i = 0; i < scale.length; ++i) {<a name="line.247"></a> <FONT color="green">248</FONT> scale[i] = scalAbsoluteTolerance + scalRelativeTolerance * Math.abs(y[i]);<a name="line.248"></a> <FONT color="green">249</FONT> }<a name="line.249"></a> <FONT color="green">250</FONT> } else {<a name="line.250"></a> <FONT color="green">251</FONT> for (int i = 0; i < scale.length; ++i) {<a name="line.251"></a> <FONT color="green">252</FONT> scale[i] = vecAbsoluteTolerance[i] + vecRelativeTolerance[i] * Math.abs(y[i]);<a name="line.252"></a> <FONT color="green">253</FONT> }<a name="line.253"></a> <FONT color="green">254</FONT> }<a name="line.254"></a> <FONT color="green">255</FONT> hNew = initializeStep(equations, forward, getOrder(), scale,<a name="line.255"></a> <FONT color="green">256</FONT> stepStart, y, yDotK[0], yTmp, yDotK[1]);<a name="line.256"></a> <FONT color="green">257</FONT> firstTime = false;<a name="line.257"></a> <FONT color="green">258</FONT> }<a name="line.258"></a> <FONT color="green">259</FONT> <a name="line.259"></a> <FONT color="green">260</FONT> stepSize = hNew;<a name="line.260"></a> <FONT color="green">261</FONT> <a name="line.261"></a> <FONT color="green">262</FONT> // next stages<a name="line.262"></a> <FONT color="green">263</FONT> for (int k = 1; k < stages; ++k) {<a name="line.263"></a> <FONT color="green">264</FONT> <a name="line.264"></a> <FONT color="green">265</FONT> for (int j = 0; j < y0.length; ++j) {<a name="line.265"></a> <FONT color="green">266</FONT> double sum = a[k-1][0] * yDotK[0][j];<a name="line.266"></a> <FONT color="green">267</FONT> for (int l = 1; l < k; ++l) {<a name="line.267"></a> <FONT color="green">268</FONT> sum += a[k-1][l] * yDotK[l][j];<a name="line.268"></a> <FONT color="green">269</FONT> }<a name="line.269"></a> <FONT color="green">270</FONT> yTmp[j] = y[j] + stepSize * sum;<a name="line.270"></a> <FONT color="green">271</FONT> }<a name="line.271"></a> <FONT color="green">272</FONT> <a name="line.272"></a> <FONT color="green">273</FONT> computeDerivatives(stepStart + c[k-1] * stepSize, yTmp, yDotK[k]);<a name="line.273"></a> <FONT color="green">274</FONT> <a name="line.274"></a> <FONT color="green">275</FONT> }<a name="line.275"></a> <FONT color="green">276</FONT> <a name="line.276"></a> <FONT color="green">277</FONT> // estimate the state at the end of the step<a name="line.277"></a> <FONT color="green">278</FONT> for (int j = 0; j < y0.length; ++j) {<a name="line.278"></a> <FONT color="green">279</FONT> double sum = b[0] * yDotK[0][j];<a name="line.279"></a> <FONT color="green">280</FONT> for (int l = 1; l < stages; ++l) {<a name="line.280"></a> <FONT color="green">281</FONT> sum += b[l] * yDotK[l][j];<a name="line.281"></a> <FONT color="green">282</FONT> }<a name="line.282"></a> <FONT color="green">283</FONT> yTmp[j] = y[j] + stepSize * sum;<a name="line.283"></a> <FONT color="green">284</FONT> }<a name="line.284"></a> <FONT color="green">285</FONT> <a name="line.285"></a> <FONT color="green">286</FONT> // estimate the error at the end of the step<a name="line.286"></a> <FONT color="green">287</FONT> error = estimateError(yDotK, y, yTmp, stepSize);<a name="line.287"></a> <FONT color="green">288</FONT> if (error <= 1.0) {<a name="line.288"></a> <FONT color="green">289</FONT> <a name="line.289"></a> <FONT color="green">290</FONT> // discrete events handling<a name="line.290"></a> <FONT color="green">291</FONT> interpolator.storeTime(stepStart + stepSize);<a name="line.291"></a> <FONT color="green">292</FONT> if (manager.evaluateStep(interpolator)) {<a name="line.292"></a> <FONT color="green">293</FONT> final double dt = manager.getEventTime() - stepStart;<a name="line.293"></a> <FONT color="green">294</FONT> if (Math.abs(dt) <= Math.ulp(stepStart)) {<a name="line.294"></a> <FONT color="green">295</FONT> // we cannot simply truncate the step, reject the current computation<a name="line.295"></a> <FONT color="green">296</FONT> // and let the loop compute another state with the truncated step.<a name="line.296"></a> <FONT color="green">297</FONT> // it is so small (much probably exactly 0 due to limited accuracy)<a name="line.297"></a> <FONT color="green">298</FONT> // that the code above would fail handling it.<a name="line.298"></a> <FONT color="green">299</FONT> // So we set up an artificial 0 size step by copying states<a name="line.299"></a> <FONT color="green">300</FONT> interpolator.storeTime(stepStart);<a name="line.300"></a> <FONT color="green">301</FONT> System.arraycopy(y, 0, yTmp, 0, y0.length);<a name="line.301"></a> <FONT color="green">302</FONT> hNew = 0;<a name="line.302"></a> <FONT color="green">303</FONT> stepSize = 0;<a name="line.303"></a> <FONT color="green">304</FONT> loop = false;<a name="line.304"></a> <FONT color="green">305</FONT> } else {<a name="line.305"></a> <FONT color="green">306</FONT> // reject the step to match exactly the next switch time<a name="line.306"></a> <FONT color="green">307</FONT> hNew = dt;<a name="line.307"></a> <FONT color="green">308</FONT> }<a name="line.308"></a> <FONT color="green">309</FONT> } else {<a name="line.309"></a> <FONT color="green">310</FONT> // accept the step<a name="line.310"></a> <FONT color="green">311</FONT> loop = false;<a name="line.311"></a> <FONT color="green">312</FONT> }<a name="line.312"></a> <FONT color="green">313</FONT> <a name="line.313"></a> <FONT color="green">314</FONT> } else {<a name="line.314"></a> <FONT color="green">315</FONT> // reject the step and attempt to reduce error by stepsize control<a name="line.315"></a> <FONT color="green">316</FONT> final double factor =<a name="line.316"></a> <FONT color="green">317</FONT> Math.min(maxGrowth,<a name="line.317"></a> <FONT color="green">318</FONT> Math.max(minReduction, safety * Math.pow(error, exp)));<a name="line.318"></a> <FONT color="green">319</FONT> hNew = filterStep(stepSize * factor, forward, false);<a name="line.319"></a> <FONT color="green">320</FONT> }<a name="line.320"></a> <FONT color="green">321</FONT> <a name="line.321"></a> <FONT color="green">322</FONT> }<a name="line.322"></a> <FONT color="green">323</FONT> <a name="line.323"></a> <FONT color="green">324</FONT> // the step has been accepted<a name="line.324"></a> <FONT color="green">325</FONT> final double nextStep = stepStart + stepSize;<a name="line.325"></a> <FONT color="green">326</FONT> System.arraycopy(yTmp, 0, y, 0, y0.length);<a name="line.326"></a> <FONT color="green">327</FONT> manager.stepAccepted(nextStep, y);<a name="line.327"></a> <FONT color="green">328</FONT> lastStep = manager.stop();<a name="line.328"></a> <FONT color="green">329</FONT> <a name="line.329"></a> <FONT color="green">330</FONT> // provide the step data to the step handler<a name="line.330"></a> <FONT color="green">331</FONT> interpolator.storeTime(nextStep);<a name="line.331"></a> <FONT color="green">332</FONT> for (StepHandler handler : stepHandlers) {<a name="line.332"></a> <FONT color="green">333</FONT> handler.handleStep(interpolator, lastStep);<a name="line.333"></a> <FONT color="green">334</FONT> }<a name="line.334"></a> <FONT color="green">335</FONT> stepStart = nextStep;<a name="line.335"></a> <FONT color="green">336</FONT> <a name="line.336"></a> <FONT color="green">337</FONT> if (fsal) {<a name="line.337"></a> <FONT color="green">338</FONT> // save the last evaluation for the next step<a name="line.338"></a> <FONT color="green">339</FONT> System.arraycopy(yDotK[stages - 1], 0, yDotK[0], 0, y0.length);<a name="line.339"></a> <FONT color="green">340</FONT> }<a name="line.340"></a> <FONT color="green">341</FONT> <a name="line.341"></a> <FONT color="green">342</FONT> if (manager.reset(stepStart, y) && ! lastStep) {<a name="line.342"></a> <FONT color="green">343</FONT> // some event handler has triggered changes that<a name="line.343"></a> <FONT color="green">344</FONT> // invalidate the derivatives, we need to recompute them<a name="line.344"></a> <FONT color="green">345</FONT> computeDerivatives(stepStart, y, yDotK[0]);<a name="line.345"></a> <FONT color="green">346</FONT> }<a name="line.346"></a> <FONT color="green">347</FONT> <a name="line.347"></a> <FONT color="green">348</FONT> if (! lastStep) {<a name="line.348"></a> <FONT color="green">349</FONT> // in some rare cases we may get here with stepSize = 0, for example<a name="line.349"></a> <FONT color="green">350</FONT> // when an event occurs at integration start, reducing the first step<a name="line.350"></a> <FONT color="green">351</FONT> // to zero; we have to reset the step to some safe non zero value<a name="line.351"></a> <FONT color="green">352</FONT> stepSize = filterStep(stepSize, forward, true);<a name="line.352"></a> <FONT color="green">353</FONT> <a name="line.353"></a> <FONT color="green">354</FONT> // stepsize control for next step<a name="line.354"></a> <FONT color="green">355</FONT> final double factor = Math.min(maxGrowth,<a name="line.355"></a> <FONT color="green">356</FONT> Math.max(minReduction,<a name="line.356"></a> <FONT color="green">357</FONT> safety * Math.pow(error, exp)));<a name="line.357"></a> <FONT color="green">358</FONT> final double scaledH = stepSize * factor;<a name="line.358"></a> <FONT color="green">359</FONT> final double nextT = stepStart + scaledH;<a name="line.359"></a> <FONT color="green">360</FONT> final boolean nextIsLast = forward ? (nextT >= t) : (nextT <= t);<a name="line.360"></a> <FONT color="green">361</FONT> hNew = filterStep(scaledH, forward, nextIsLast);<a name="line.361"></a> <FONT color="green">362</FONT> }<a name="line.362"></a> <FONT color="green">363</FONT> <a name="line.363"></a> <FONT color="green">364</FONT> }<a name="line.364"></a> <FONT color="green">365</FONT> <a name="line.365"></a> <FONT color="green">366</FONT> final double stopTime = stepStart;<a name="line.366"></a> <FONT color="green">367</FONT> resetInternalState();<a name="line.367"></a> <FONT color="green">368</FONT> return stopTime;<a name="line.368"></a> <FONT color="green">369</FONT> <a name="line.369"></a> <FONT color="green">370</FONT> }<a name="line.370"></a> <FONT color="green">371</FONT> <a name="line.371"></a> <FONT color="green">372</FONT> /** Get the minimal reduction factor for stepsize control.<a name="line.372"></a> <FONT color="green">373</FONT> * @return minimal reduction factor<a name="line.373"></a> <FONT color="green">374</FONT> */<a name="line.374"></a> <FONT color="green">375</FONT> public double getMinReduction() {<a name="line.375"></a> <FONT color="green">376</FONT> return minReduction;<a name="line.376"></a> <FONT color="green">377</FONT> }<a name="line.377"></a> <FONT color="green">378</FONT> <a name="line.378"></a> <FONT color="green">379</FONT> /** Set the minimal reduction factor for stepsize control.<a name="line.379"></a> <FONT color="green">380</FONT> * @param minReduction minimal reduction factor<a name="line.380"></a> <FONT color="green">381</FONT> */<a name="line.381"></a> <FONT color="green">382</FONT> public void setMinReduction(final double minReduction) {<a name="line.382"></a> <FONT color="green">383</FONT> this.minReduction = minReduction;<a name="line.383"></a> <FONT color="green">384</FONT> }<a name="line.384"></a> <FONT color="green">385</FONT> <a name="line.385"></a> <FONT color="green">386</FONT> /** Get the maximal growth factor for stepsize control.<a name="line.386"></a> <FONT color="green">387</FONT> * @return maximal growth factor<a name="line.387"></a> <FONT color="green">388</FONT> */<a name="line.388"></a> <FONT color="green">389</FONT> public double getMaxGrowth() {<a name="line.389"></a> <FONT color="green">390</FONT> return maxGrowth;<a name="line.390"></a> <FONT color="green">391</FONT> }<a name="line.391"></a> <FONT color="green">392</FONT> <a name="line.392"></a> <FONT color="green">393</FONT> /** Set the maximal growth factor for stepsize control.<a name="line.393"></a> <FONT color="green">394</FONT> * @param maxGrowth maximal growth factor<a name="line.394"></a> <FONT color="green">395</FONT> */<a name="line.395"></a> <FONT color="green">396</FONT> public void setMaxGrowth(final double maxGrowth) {<a name="line.396"></a> <FONT color="green">397</FONT> this.maxGrowth = maxGrowth;<a name="line.397"></a> <FONT color="green">398</FONT> }<a name="line.398"></a> <FONT color="green">399</FONT> <a name="line.399"></a> <FONT color="green">400</FONT> /** Compute the error ratio.<a name="line.400"></a> <FONT color="green">401</FONT> * @param yDotK derivatives computed during the first stages<a name="line.401"></a> <FONT color="green">402</FONT> * @param y0 estimate of the step at the start of the step<a name="line.402"></a> <FONT color="green">403</FONT> * @param y1 estimate of the step at the end of the step<a name="line.403"></a> <FONT color="green">404</FONT> * @param h current step<a name="line.404"></a> <FONT color="green">405</FONT> * @return error ratio, greater than 1 if step should be rejected<a name="line.405"></a> <FONT color="green">406</FONT> */<a name="line.406"></a> <FONT color="green">407</FONT> protected abstract double estimateError(double[][] yDotK,<a name="line.407"></a> <FONT color="green">408</FONT> double[] y0, double[] y1,<a name="line.408"></a> <FONT color="green">409</FONT> double h);<a name="line.409"></a> <FONT color="green">410</FONT> <a name="line.410"></a> <FONT color="green">411</FONT> }<a name="line.411"></a> </PRE> </BODY> </HTML>