001/* An actor that outputs the difference between successive inputs.
002
003 Copyright (c) 1998-2014 The Regents of the University of California.
004 All rights reserved.
005 Permission is hereby granted, without written agreement and without
006 license or royalty fees, to use, copy, modify, and distribute this
007 software and its documentation for any purpose, provided that the above
008 copyright notice and the following two paragraphs appear in all copies
009 of this software.
010
011 IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
012 FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
013 ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
014 THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
015 SUCH DAMAGE.
016
017 THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
018 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
019 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
020 PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
021 CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
022 ENHANCEMENTS, OR MODIFICATIONS.
023
024 PT_COPYRIGHT_VERSION_2
025 COPYRIGHTENDKEY
026
027 */
028package ptolemy.actor.lib;
029
030import ptolemy.data.Token;
031import ptolemy.kernel.CompositeEntity;
032import ptolemy.kernel.util.IllegalActionException;
033import ptolemy.kernel.util.NameDuplicationException;
034
035///////////////////////////////////////////////////////////////////
036//// Differential
037
038/**
039 Output the current input minus the previous input, or if there
040 has been no previous input, the current input itself.
041
042 @author Edward A. Lee
043 @version $Id$
044 @since Ptolemy II 2.0
045 @Pt.ProposedRating Red (eal)
046 @Pt.AcceptedRating Red (cxh)
047 */
048public class Differential extends Transformer {
049    /** Construct an actor with the given container and name.
050     *  @param container The container.
051     *  @param name The name of this actor.
052     *  @exception IllegalActionException If the actor cannot be contained
053     *   by the proposed container.
054     *  @exception NameDuplicationException If the container already has an
055     *   actor with this name.
056     */
057    public Differential(CompositeEntity container, String name)
058            throws NameDuplicationException, IllegalActionException {
059        super(container, name);
060    }
061
062    ///////////////////////////////////////////////////////////////////
063    ////                         public methods                    ////
064
065    /** Consume at most one token from the <i>input</i> port and output
066     *  its value minus the value of the input read in the previous
067     *  iteration.  If there has been no previous iteration, then
068     *  output the current input.  If there is no input, then produce
069     *  no output.
070     *  @exception IllegalActionException If subtraction is not
071     *   supported by the supplied tokens.
072     */
073    @Override
074    public void fire() throws IllegalActionException {
075        super.fire();
076        if (input.hasToken(0)) {
077            _currentInput = input.get(0);
078
079            if (_lastInput != null) {
080                output.broadcast(_currentInput.subtract(_lastInput));
081            } else {
082                output.broadcast(_currentInput);
083            }
084        }
085    }
086
087    /** Reset to indicate that no input has yet been seen.
088     *  @exception IllegalActionException If the parent class throws it.
089     */
090    @Override
091    public void initialize() throws IllegalActionException {
092        super.initialize();
093        _lastInput = null;
094    }
095
096    /** Record the most recent input as the latest input.
097     *  @exception IllegalActionException If the base class throws it.
098     */
099    @Override
100    public boolean postfire() throws IllegalActionException {
101        _lastInput = _currentInput;
102        return super.postfire();
103    }
104
105    ///////////////////////////////////////////////////////////////////
106    ////                         private members                   ////
107    private Token _currentInput;
108
109    private Token _lastInput;
110}