ModelPolynomial

java.lang.Object
- org.ptolemy.qss.util.ModelPolynomial

```
public final class ModelPolynomial
extends java.lang.Object
```
Model of a variable that changes with time, using a polynomial.
Represent a polynomial model:

xModel{t} = c0 + c1*dt + c2*dt^2 + ...

where
- xModel{t}, model of some scalar variable x, as a function of time.
- t, time of interest.
- dt = t - tModel, time difference.
- tModel, time of model formation.
- c0, c1, c2, ..., model coefficients. The first coefficient is the value of x at tModel. The remaining coefficients are related to derivatives of x at tModel by ci = (1/i!)(d^i x/dt^i)(tModel). That is, they are the coefficients of the Taylor series expansion.
- The notation g{y} means that g is a function of y.
Need for a model time

Each ModelPolynomial object needs to have an associated simulation time, in order to define the model. Add this simulation time by setting field this.tModel to the desired Time object. Failing to do so will cause a NullPointerException for most of the useful methods on this class.

Alternative designs that would enforce this condition include:
- Add a Time object to the constructor. This design was rejected because it implies that the model time is fixed, and should not be changed during the lifetime of the model.
- Allocate a new Time object, with a default time, when constructing a ModelPoly object. This design was rejected because class Time is meant to be able to be swapped with other implementations, which may have different constructor needs.
Purpose

This class is meant to provide a lightweight capability for working with and exchanging models. The majority of data are kept public, in order to facilitate changing model coefficients without the overhead of accessor (setter, getter) calls.

The design intention is that multiple objects in a system can share a single ModelPolynomial, in order to share a model of a common variable. In principle, at any given simulation time, only one of those objects should have "write access", and it alone should set the model parameters. The other objects in the system can use the model, but should refrain from changing it.

Note that the ModelPolynomial object does nothing to enforce cooperation among readers and writers. It does, however, provide a simple counter for how many objects claim write access. This allows objects that intend to cooperate to double-check that they are doing so correctly.
Since:

Ptolemy II 11.0

Version:

$id$

Author:

David M. Lorenzetti. Contributor: Edward A. Lee

Pt.AcceptedRating:

red (reviewmoderator) // FIXME: Fill in.

Pt.ProposedRating:

red (dmlorenzetti)

Field Summary

Fields
Modifier and Type	Field and Description
`double[]`	`coeffs` Polynomial coefficients, in order: [c0, c1, c2, ...].
`Time`	`tModel` Simulation time at which model was formed, such that xModel{tModel} = c0.

Constructor Summary

Constructors
Constructor and Description

ModelPolynomial(int maxOrder)
Construct a ModelPolynomial.

Constructors
Constructor and Description
`ModelPolynomial(int maxOrder)` Construct a `ModelPolynomial`.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`claimWriteAccess()` Claim write access.
`double`	`evaluate(double dt)` Evaluate the model at a delta-time.
`double`	`evaluate(Time simTime)` Evaluate the model at a simulation time.
`double`	`evaluateDerivative(double dt)` Evaluate d{model}/d{t} at a delta-time.
`double`	`evaluateDerivative(Time simTime)` Evaluate d{model}/d{t} at a simulation time.
`double`	`evaluateDerivative2(double dt)` Evaluate d^2{model}/d{t}^2 at a delta-time.
`double`	`evaluateDerivative2(Time simTime)` Evaluate d^2{model}/d{t}^2 at a simulation time.
`int`	`getMaximumOrder()` Get the maximum order of the polynomial.
`int`	`getWriterCount()` Find out how many objects claim write access.
`int`	`releaseWriteAccess()` Release claim of write access.
`java.lang.String`	`toString()` Return a string representation of the model.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - tModel
```
public Time tModel
```
    Simulation time at which model was formed, such that xModel{tModel} = c0.
  - coeffs
```
public final double[] coeffs
```
    Polynomial coefficients, in order: [c0, c1, c2, ...].
- Constructor Detail
  - ModelPolynomial
```
public ModelPolynomial(int maxOrder)
```
    Construct a ModelPolynomial.
    
    Parameters:
    
    maxOrder - Maximum order of the polynomial (0=constant, 1=line, etc).
- Method Detail
  - claimWriteAccess
```
public final int claimWriteAccess()
```
    Claim write access.
    
    Returns:
    
    Count of all unique claims of write access (including caller).
  - evaluate
```
public final double evaluate(Time simTime)
```
    Evaluate the model at a simulation time.
    
    Parameters:
    
    simTime - Simulation time at which to evaluate the model.
    
    Returns:
    
    The model evaluated at a simulation time.
  - evaluate
```
public final double evaluate(double dt)
```
    Evaluate the model at a delta-time.
    
    Parameters:
    
    dt - Difference (simTime - tModel) at which to evaluate the model.
    
    Returns:
    
    The model evaluated at a delta-time.
  - evaluateDerivative
```
public final double evaluateDerivative(Time simTime)
```
    Evaluate d{model}/d{t} at a simulation time.
    
    Parameters:
    
    simTime - Simulation time at which to evaluate the derivative.
    
    Returns:
    
    The model derivative evaluated at a simulation time.
  - evaluateDerivative
```
public final double evaluateDerivative(double dt)
```
    Evaluate d{model}/d{t} at a delta-time.
    
    Parameters:
    
    dt - Difference (simTime - tModel) at which to evaluate the derivative.
    
    Returns:
    
    The model derivative evaluated at a delta-time.
  - evaluateDerivative2
```
public final double evaluateDerivative2(Time simTime)
```
    Evaluate d^2{model}/d{t}^2 at a simulation time.
    
    Parameters:
    
    simTime - Simulation time at which to evaluate the derivative.
    
    Returns:
    
    The model second derivative evaluated at a simulation time.
  - evaluateDerivative2
```
public final double evaluateDerivative2(double dt)
```
    Evaluate d^2{model}/d{t}^2 at a delta-time.
    
    Parameters:
    
    dt - Difference (simTime - tModel) at which to evaluate the derivative.
    
    Returns:
    
    The model second derivative evaluated at a delta-time.
  - getMaximumOrder
```
public final int getMaximumOrder()
```
    Get the maximum order of the polynomial.
    
    Returns:
    
    The maximum order of the polynomial.
  - getWriterCount
```
public final int getWriterCount()
```
    Find out how many objects claim write access.
    
    Returns:
    
    The number of objects that claim write access.
  - releaseWriteAccess
```
public final int releaseWriteAccess()
```
    Release claim of write access.
    
    Returns:
    
    Count of all remaining claims of write access.
  - toString
```
public final java.lang.String toString()
```
    Return a string representation of the model.
    
    Overrides:
    
    toString in class java.lang.Object
    
    Returns:
    
    The string representation of the model.

Class ModelPolynomial

Need for a model time

Purpose

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

tModel

coeffs

Constructor Detail

ModelPolynomial

Method Detail

claimWriteAccess

evaluate

evaluate

evaluateDerivative

evaluateDerivative

evaluateDerivative2

evaluateDerivative2

getMaximumOrder

getWriterCount

releaseWriteAccess

toString