org.jscience.physics.nuclear.kinematics.math.analysis
Class NonLinearFit

java.lang.Object
  extended by org.jscience.physics.nuclear.kinematics.math.analysis.NonLinearFit
Direct Known Subclasses:
GaussianFit

public abstract class NonLinearFit
extends java.lang.Object

This abstract class uses LevenbergMarquadt to do non-linear parametric function fitting. An actual class should define additional parameters and add them to parameters, It should implement estimate(), valueAt(), and derivative().

See Also:
valueAt(double), derivative(double, java.lang.String), Fit, LevenbergMarquadt, GaussianFit, Fit#estimate

Field Summary
protected  Parameter chisq
          the calculated reduced chi-squared statistic
protected  double[] counts
          The histogram to be fitted.
protected  double[] errors
          The errors associatied with counts.
protected  LevenbergMarquadt lm
          does the actual matrix algebra to find the best fit
protected  int maxCH
          the int value of hi
protected  int minCH
          the int value of lo
 
Constructor Summary
NonLinearFit(double[] spectrum, double[] errors, int minCh, int maxCh)
          Class constructor.
 
Method Summary
protected  void addParameter(Parameter newParameter)
          Makes a parameterTable from parameters.
 double calculate(int channel)
          Calculate function value for specific channel in the histogram.
abstract  double derivative(double x, java.lang.String parameterName)
          Evaluates derivative with respect to parameterName at x.
 java.lang.String doFit()
          Perform fit calulation and return a status String.
abstract  void estimate()
          Estimate parameters for which the user requests estimation.
 Parameter getParameter(java.lang.String which)
          Allows access to parameters by name for modification.
 double p(java.lang.String which)
          Returns double value of parameter indicated by name.
 void setParameter(java.lang.String which, double value)
          Set a parameter designated by name to a new value.
abstract  double valueAt(double x)
          Evaluates at x for given parameters.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

counts

protected double[] counts
The histogram to be fitted.


errors

protected double[] errors
The errors associatied with counts.


lm

protected LevenbergMarquadt lm
does the actual matrix algebra to find the best fit


chisq

protected Parameter chisq
the calculated reduced chi-squared statistic


minCH

protected int minCH
the int value of lo


maxCH

protected int maxCH
the int value of hi

Constructor Detail

NonLinearFit

public NonLinearFit(double[] spectrum,
                    double[] errors,
                    int minCh,
                    int maxCh)
Class constructor. This is still an abstract class. Specific subclass constructors will call this before executing their own constructors.

Method Detail

addParameter

protected void addParameter(Parameter newParameter)
Makes a parameterTable from parameters.

See Also:
parameterTable, parameters

estimate

public abstract void estimate()
                       throws FitException
Estimate parameters for which the user requests estimation. Unnecessary to implement, but very useful since good guesses are usually needed to find the fit.

Throws:
FitException - thrown if unrecoverable error occurs during estimation

valueAt

public abstract double valueAt(double x)
Evaluates at x for given parameters.

Parameters:
x - value at which to evaluate the fit function
Returns:
value of fit function at x

derivative

public abstract double derivative(double x,
                                  java.lang.String parameterName)
Evaluates derivative with respect to parameterName at x.

Parameters:
parameterName - the name of the parameter to differentiate with respect to
x - value to evalueate at
Returns:
df(x)/d(parameterName) at x

doFit

public java.lang.String doFit()
                       throws FitException
Perform fit calulation and return a status String. Calls LevenbergMarquadt several times, which determines changes in parameter values likely to reduce chi-squared. When reductions are no longer significant, it stops. If there is no covergence, it stops after 10 iterations.

Returns:
message with number of iterations and degrees of freedom to fit
Throws:
FitException - thrown if unrecoverable error occurs during fit

p

public double p(java.lang.String which)
Returns double value of parameter indicated by name.

Parameters:
which - the name of the parameter
Returns:
the current value of the parameter

setParameter

public void setParameter(java.lang.String which,
                         double value)
                  throws FitException
Set a parameter designated by name to a new value.

Parameters:
which - the name of the parameter
value - the value to assign
Throws:
FitException - thrown if unrecoverable error occurs

getParameter

public Parameter getParameter(java.lang.String which)
Allows access to parameters by name for modification.

Parameters:
which - the name of the parameter
Returns:
the Parameter object

calculate

public double calculate(int channel)
Calculate function value for specific channel in the histogram.

Parameters:
channel - the channel to evaluate the function at
Returns:
the value of the function at channel