Fix RK solver to avoid getting stuck when derivatives are estimated using finite difference (e.g. in the sine modulated population model). Introduce a min step allowed. TODO: Make it a parameter of the solver

git-svn-id: http://dev.eclipse.org/svnroot/technology/org.eclipse.stem/branches/STEM_1_4_0@3452 92a21009-5b66-0410-b83a-dc787c41c6e9

core/org.eclipse.stem.solvers.rk/src/org/eclipse/stem/solvers/rk/impl/RungeKuttaImpl.java

diff --git a/core/org.eclipse.stem.solvers.rk/src/org/eclipse/stem/solvers/rk/impl/RungeKuttaImpl.java b/core/org.eclipse.stem.solvers.rk/src/org/eclipse/stem/solvers/rk/impl/RungeKuttaImpl.java
index c86f580..2cddb84 100644
--- a/core/org.eclipse.stem.solvers.rk/src/org/eclipse/stem/solvers/rk/impl/RungeKuttaImpl.java
+++ b/core/org.eclipse.stem.solvers.rk/src/org/eclipse/stem/solvers/rk/impl/RungeKuttaImpl.java
@@ -91,6 +91,12 @@
 	static double SAFETY=0.9, PGROW=-0.2, PSHRNK=-0.25, ERRCON=1.89E-4;

 	static double TINY = 1E-30;

 

+	// For 1.4 release. When derivatives are estimated (e.g. using a finite difference method) the solver risk getting stuck. We

+	// introduce a minimal step size allowed to force it out of these situations.

+	// TODO: Make this a parameter of the RK solver

+	

+	static double MIN_STEP = 1E-15;

+	

 	private static int MAX_PROGRESS_REPORTS = 5;

 	

 	/**

@@ -831,6 +837,7 @@
 					yout.add(currentValue);

 								

 					

+					

 					// Get the error

 					k1.set(k1map.get(diseaseLabel));

 					k3.set(k3map.get(diseaseLabel));

@@ -852,10 +859,15 @@
 					double error = yerror.max();

 					error /= getRelativeTolerance();

 					

+					// If min step reached, force it to accept the step and increase the step size below

+					if(h < MIN_STEP)

+						error = ERRCON;

+					

 					if(error > maxerror) {

 						maxerror = error;

 					}

 					

+					

 					if(error <= 1.0) 

 						finalEstimate.put(diseaseLabel, 

 							(IntegrationLabelValue)yout.copy());