[Repast-interest] Error Using System Dynamics in Repast

[yutaoz <yu...@gm...>]

Hi,

I am trying to incorporate some system dynamics into a agent-based model I
am building using plain Java in Repast.

I tried the directions on 
http://repast.sourceforge.net/docs/reference/SIM/Using%20Systems%20Dynamics.html
System Dynamics  to write this code:

import repast.simphony.engine.schedule.ScheduledMethod;
import repast.simphony.systemsdynamics.Formula;
import repast.simphony.systemsdynamics.Formula.Type;
public class District{
	public double sta, sec;
	public Formula formula1;
	public District(){
		super();
		sta=0.5;
		sec=0.5;
		formula1=new Formula(this, "sta", "sec*dsec", Type.EQUATION);
	}
	@ScheduledMethod(start = 1, interval = 1)
	public void step(){
		sec=sec+0.1;
	}
}

and received the following error:
2009/07/10 12:48:51,538: Error while initializing simulation
java.lang.NullPointerException
	at
repast.simphony.engine.schedule.AbstractAction.<init>(AbstractAction.java:95)
	at repast.simphony.systemsdynamics.Formula.<init>(Formula.java:62)
	at repast.simphony.systemsdynamics.Formula.<init>(Formula.java:38)
	at psir.districtcontext.District.<init>(District.java:18)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown
Source)
	at java.lang.reflect.Constructor.newInstance(Unknown Source)
	at java.lang.Class.newInstance0(Unknown Source)
	at java.lang.Class.newInstance(Unknown Source)
	at repast.simphony.space.gis.ShapefileLoader.next(ShapefileLoader.java:145)
	at psir.districtcontext.DistrictContext.<init>(DistrictContext.java:37)
	at psir.ContextCreator.build(ContextCreator.java:24)
	at
repast.simphony.dataLoader.engine.ClassNameContextBuilder.build(ClassNameContextBuilder.java:39)
	at
repast.simphony.dataLoader.engine.DataLoaderControllerAction.runInitialize(DataLoaderControllerAction.java:51)
	at
repast.simphony.engine.controller.DefaultController$2.visit(DefaultController.java:171)
	at
repast.simphony.engine.controller.DefaultController$2.visit(DefaultController.java:1)
	at
repast.simphony.util.collections.NaryTree.preOrderTraverals(NaryTree.java:287)
	at
repast.simphony.util.collections.NaryTree.preOrderTraverals(NaryTree.java:290)
	at
repast.simphony.util.collections.NaryTree.preOrderTraverals(NaryTree.java:290)
	at
repast.simphony.util.collections.NaryTree.preOrderTraversal(NaryTree.java:283)
	at
repast.simphony.engine.controller.DefaultController.runInitialize(DefaultController.java:169)
	at
repast.simphony.engine.controller.DefaultController.runInitialize(DefaultController.java:324)
	at repast.simphony.ui.RSApplication.initSim(RSApplication.java:134)
	at repast.simphony.ui.action.InitRun.actionPerformed(InitRun.java:17)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
	at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
	at java.awt.Component.processMouseEvent(Unknown Source)
	at javax.swing.JComponent.processMouseEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

Obviously, something was not initiated correctly, but I can't see what
exactly.
Any help is appreciated.

Thanks,
Tao
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