Package ptolemy.actor.lib

Class LinearDifferenceEquationSystem

  • All Implemented Interfaces:
    java.lang.Cloneable, Actor, Executable, FiringsRecordable, Initializable, TypedActor, Changeable, Debuggable, DebugListener, Derivable, Instantiable, ModelErrorHandler, MoMLExportable, Moveable, Nameable
    public class LinearDifferenceEquationSystem
extends Transformer
    Linear Difference Equation System.

    The linear state-space model implements a system whose behavior is defined by: 

     x(k+1) = Ax(k) + Bu(k)
 y(k) = Cx(k) + Du(k)
 x(0) = x0
    where x is the state vector, u is the input vector, and y is the output vector. (Note that in Ptolemy II, vectors are double matrices with one column or one row.) The matrix coefficients must have the following characteristics: 
     A must be an n-by-n matrix, where n is the number of states.
 B must be an n-by-m matrix, where m is the number of inputs.
 C must be an r-by-n matrix, where r is the number of outputs.
 D must be an r-by-m matrix.
    For each firing, the actor accepts one input DoubleMatrixToken of dimension m x 1, and generates one output DoubleMatrixToken of dimension r x 1.

    In addition to producing the output y through port output, the actor also produce the state values x through port state.

    Since:
    Ptolemy II 2.0
    Version:
    $Id$
    Author:
    Jie Liu and Elaine Cheong
    Pt.AcceptedRating:
    Yellow (celaine)
    Pt.ProposedRating:
    Yellow (celaine)

    • Field Detail

      • state

        public TypedIOPort state
        Output port that produces DoubleMatrixToken of dimension r x 1 (see class comment).

      • A

        public Parameter A
        The A matrix in the state-space representation. It must be a square matrix. The default value is [[1.0]].

      • B

        public Parameter B
        The B matrix in the state-space representation. The number of rows must be equal to the number of rows of the A matrix. The number of columns must be equal to the number of rows in the input token. The default value is [[1.0]].

      • C

        public Parameter C
        The C matrix in the state-space representation. The number of columns must be equal to the number of columns of the A matrix. The number of rows must be equal to the number of columns in the output token. The default value is [[0.0]].

      • D

        public Parameter D
        The D matrix in the state-space representation. The number of columns must be equal to the number of rows in the input token (a DoubleMatrixToken of dimension m x 1. The number of rows must be equal to the number of columns in the output token (a DoubleMatrixToken of dimension r x 1. The default value is [[0.0]].

      • initialStates

        public Parameter initialStates
        The initial condition for the state variables. This must be a column vector (double matrix with only one column) whose length is equal to the number of state variables. The default value is [0.0]. NOTE: Changes to this parameter will be * applied at the next time when fire() is called.

    • Method Detail

      • attributeChanged

        public void attributeChanged​(Attribute attribute)
                      throws IllegalActionException
        If the argument is A, B, C, D or initialStates parameters, check that they are indeed matrices and vectors, and request initialization from the director if there is one. Other sanity checks like the dimensions of the matrices will be done in the preinitialize() method.
        Overrides:
        attributeChanged in class NamedObj
        Parameters:
        attribute - The attribute that changed.
        Throws:
        IllegalActionException - If the numerator and the denominator matrix is not a row vector.

      • fire

        public void fire()
          throws IllegalActionException
        Consume the input token, compute the system response, and produce outputs. Notice that the state is updated in postfire. That is, if fire() is called multiple times before postfire() is called, this actor will use the same internal state to compute the outputs.
        Specified by:
        fire in interface Executable
        Overrides:
        fire in class AtomicActor<TypedIOPort>
        Throws:
        IllegalActionException - If the get() or send() methods of the ports throw this exception.

      • prefire

        public boolean prefire()
                throws IllegalActionException
        If the parameter initialStates has changed, then update the internal state of this actor to be the value of the initialStates parameter.
        Specified by:
        prefire in interface Executable
        Overrides:
        prefire in class AtomicActor<TypedIOPort>
        Returns:
        True if this actor is ready for firing, false otherwise.
        Throws:
        IllegalActionException - If initialStates parameter is invalid, or if the base class throws it.

      • preinitialize

        public void preinitialize()
                   throws IllegalActionException
        Check the dimension of all parameters. If the system needs multiple inputs, then set the type of the input port to be DoubleMatrix; otherwise set the type to Double. Similarly, for the output ports output and state, if the system needs multiple outputs, then set the type of the port to be DoubleMatrix; otherwise set the type to Double.
        Specified by:
        preinitialize in interface Initializable
        Overrides:
        preinitialize in class AtomicActor<TypedIOPort>
        Throws:
        IllegalActionException - If the dimensions do not match.