/* An actor that outputs the discrete derivative between successive inputs.
Copyright (c) 1998-2005 The Regents of the University of California.
All rights reserved.
Permission is hereby granted, without written agreement and without
license or royalty fees, to use, copy, modify, and distribute this
software and its documentation for any purpose, provided that the above
copyright notice and the following two paragraphs appear in all copies
of this software.
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
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*/
package ptolemy.domains.de.lib;
import ptolemy.actor.TypedIOPort;
import ptolemy.actor.util.Time;
import ptolemy.actor.util.TimedEvent;
import ptolemy.data.DoubleToken;
import ptolemy.data.type.BaseType.DoubleType;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.NameDuplicationException;
import ptolemy.kernel.util.Workspace;
//////////////////////////////////////////////////////////////////////////
//// Derivative
/**
Output the discrete derivative of the input, y[n] = (x[n] - x[n-1])/dt,
where <i>dt</i> is the time gap between input events. Output is not generated
until two inputs have been consumed.
<p>
The output of this actor is constrained to be a double, and input must be castable
to a double. If the input signal is not left-continuous, the derivative will be either
infinite or undefined and an exception is thrown.
<p>
In postfire(), if an event is present on the <i>reset</i> port, this
actor resets to its initial state, and will not output until two
subsequent inputs have been consumed. This is useful if the input signal is
switched on and off, in which case the time gap between events becomes large
and would otherwise effect the value of the derivative for one sample.
<p>
@author Jeff C. Jensen
@version $Id: Derivative.java$
@since Ptolemy II 8.1
@see ptolemy.actor.lib.Differential
*/
public class Derivative extends DETransformer {
/** Construct an actor with the given container and name.
* @param container The container.
* @param name The name of this actor.
* @exception IllegalActionException If the actor cannot be contained
* by the proposed container.
* @exception NameDuplicationException If the container already has an
* actor with this name.
*/
public Derivative(CompositeEntity container, String name)
throws NameDuplicationException, IllegalActionException {
super(container, name);
reset = new TypedIOPort(this, "reset", true, false);
reset.setMultiport(true);
input.setTypeAtMost(DoubleType.DOUBLE);
output.setTypeEquals(DoubleType.DOUBLE);
}
///////////////////////////////////////////////////////////////////
//// public methods ////
/** Clone the actor into the specified workspace. This calls the
* base class and then sets the ports.
* @param workspace The workspace for the new object.
* @return A new actor.
* @exception CloneNotSupportedException If a derived class has
* has an attribute that cannot be cloned.
*/
public Object clone(Workspace workspace) throws CloneNotSupportedException {
Derivative newObject = (Derivative) super.clone(workspace);
newObject.input.setTypeAtMost(DoubleType.DOUBLE);
newObject.output.setTypeEquals(DoubleType.DOUBLE);
// This is not strictly needed (since it is always recreated
// in preinitialize) but it is safer.
newObject._lastInput = null;
return newObject;
}
/** Consume at most one token from the <i>input</i> port and output
* its value minus the value of the input read in the previous
* iteration, divided by the time gap between the two events.
* If there has been no previous iteration, no output is sent.
* If there is no input, then produce no output.
* @exception IllegalActionException If subtraction or division is not
* supported by the supplied tokens.
*/
public void fire() throws IllegalActionException {
super.fire();
if (input.hasToken(0)) {
Time currentTime = getDirector().getModelTime();
DoubleToken currentToken = (DoubleToken)input.get(0);
_currentInput = new TimedEvent(currentTime, currentToken);
if (_lastInput != null) {
Time lastTime = _lastInput.timeStamp;
DoubleToken lastToken = (DoubleToken)_lastInput.contents;
DoubleToken timeGap = new DoubleToken(currentTime.subtract(lastTime).getDoubleValue());
//If the timeGap is zero, then we have received a simultaneous event. If the
// value of the input has not changed, then we can ignore this input, as a control
// signal was already generated. However if the value has changed, then the signal
// is discontinuous and an exception will be thrown.
if (timeGap.doubleValue() == 0 && !currentToken.equals(lastToken)){
throw new IllegalActionException("Derivative received discontinuous input.");
}
output.broadcast(currentToken.subtract(lastToken).divide(timeGap));
}
}
}
/** Reset to indicate that no input has yet been seen.
* @exception IllegalActionException If the parent class throws it.
*/
public void initialize() throws IllegalActionException {
super.initialize();
_lastInput = null;
_currentInput = null;
}
/** Record the most recent input as the latest input. If a reset
* event has been received, process it here.
* @exception IllegalActionException If the base class throws it.
*/
public boolean postfire() throws IllegalActionException {
//If reset port is connected and has a token, reset state.
if(reset.getWidth() > 0){
if(reset.hasToken(0)){
//Consume reset token
reset.get(0);
//Reset the current input
_currentInput = null;
}
}
_lastInput = _currentInput;
return super.postfire();
}
///////////////////////////////////////////////////////////////////
//// ports and parameters ////
/** The reset port, which has undeclared type. If this port
* receives a token, this actor resets to its initial state,
* and no output is generated until two inputs have been received.
*/
public TypedIOPort reset;
///////////////////////////////////////////////////////////////////
//// private members ////
private TimedEvent _currentInput;
private TimedEvent _lastInput;
}