BCGraphFitter Class Reference

#include <BCGraphFitter.h>

Inheritance diagram for BCGraphFitter:

[legend]

Collaboration diagram for BCGraphFitter:

[legend]

List of all members.

---

Detailed Description

A class for fitting graphs with functions.

Author:

Daniel Kollar

Kevin Kröninger

Version:

1.0

Date:

2008 This class allows fitting of a TGraphErrors using a TF1 function. It doeasn't take the x uncertainties into account. For that look at BCGraphXFitter (not yet implemented).

Definition at line 34 of file BCGraphFitter.h.

Public Member Functions
Constructors and destructors
	BCGraphFitter (TGraphErrors *graph, TF1 *func)
	BCGraphFitter ()
	~BCGraphFitter ()
Member functions (miscellaneous methods)
void	DrawFit (const char *options="", bool flaglegend=false)
int	Fit (TGraphErrors *graph, TF1 *func)
int	Fit ()
double	FitFunction (std::vector< double > x, std::vector< double > parameters)
double	LogAPrioriProbability (std::vector< double > parameters)
double	LogLikelihood (std::vector< double > parameters)
Member functions (get)
TGraph *	GetErrorBand ()
TF1 *	GetFitFunction ()
TGraphErrors *	GetGraph ()
TGraph *	GetGraphFitFunction ()
Member functions (set)
int	SetFitFunction (TF1 *func)
int	SetGraph (TGraphErrors *graph)
Private Attributes
TGraph *	fErrorBand
TF1 *	fFitFunction
TGraphErrors *	fGraph
TGraph *	fGraphFitFunction

---

Constructor & Destructor Documentation

BCGraphFitter::BCGraphFitter

(

)

Default constructor

Definition at line 25 of file BCGraphFitter.cxx.

                             : BCModel("GraphFitter")
{
   fGraph = 0;
   fFitFunction = 0;
   fErrorBand = 0;
   fGraphFitFunction = 0;

   this -> MCMCSetNIterationsRun(2000);

   this -> SetFillErrorBand();
}

BCGraphFitter::BCGraphFitter	(	TGraphErrors *	graph,
		TF1 *	func
	)

Constructor

Parameters:

	graph	pointer to TGraphErrors
	func	pointer to TF1

Definition at line 39 of file BCGraphFitter.cxx.

                                                             : BCModel("GraphFitter")
{
   fGraph = 0;
   fFitFunction = 0;
   fErrorBand = 0;
   fGraphFitFunction = 0;

   this -> MCMCSetNIterationsRun(2000);

   this -> SetGraph(graph);
   this -> SetFitFunction(func);

   this -> SetFillErrorBand();
}

BCGraphFitter::~BCGraphFitter

(

)

The default destructor.

Definition at line 179 of file BCGraphFitter.cxx.

{}

---

Member Function Documentation

void BCGraphFitter::DrawFit	(	const char *	options = "",
		bool	flaglegend = false
	)

Draw the fit in the current pad.

Definition at line 270 of file BCGraphFitter.cxx.

{
   if (!fGraph)
   {
      BCLog::Out(BCLog::error, BCLog::error,"BCGraphFitter::DrawFit() : TGraphErrors not defined.");
      return;
   }

   if (!fFitFunction)
   {
      BCLog::Out(BCLog::error, BCLog::error,"BCGraphFitter::DrawFit() : Fit function not defined.");
      return;
   }

   // check wheather options contain "same"
   TString opt = options;
   opt.ToLower();

   // if not same, draw the histogram first to get the axes
   if(!opt.Contains("same"))
      fGraph -> Draw("ap");

   // draw the error band as central 68% probability interval
   fErrorBand = this -> GetErrorBandGraph(0.16, 0.84);
   fErrorBand -> Draw("f same");

   // draw the fit function on top
   fGraphFitFunction = this -> GetFitFunctionGraph( this->GetBestFitParameters() );
   fGraphFitFunction -> SetLineColor(kRed);
   fGraphFitFunction -> SetLineWidth(2);
   fGraphFitFunction -> Draw("l same");

   // now draw the histogram again since it was covered by the band and
   // the best fit
   fGraph -> Draw("p same");

   // draw legend
   if (flaglegend)
   {
      TLegend * legend = new TLegend(0.25, 0.75, 0.55, 0.95);
      legend -> SetBorderSize(0);
      legend -> SetFillColor(kWhite);
      legend -> AddEntry(fGraph, "Data", "P");
      legend -> AddEntry(fGraphFitFunction, "Best fit", "L");
      legend -> AddEntry(fErrorBand, "Error band", "F");
      legend -> Draw();
   }

   gPad -> RedrawAxis();
}

int BCGraphFitter::Fit	(	TGraphErrors *	graph,
		TF1 *	func
	)

Performs the fit of the graph with the function.

Parameters:

	graph	pointer to TGraphErrors object
	func	pointer to TF1 object

Returns:

An error code.

Definition at line 240 of file BCGraphFitter.cxx.

{
   // set graph
   if (!this -> SetGraph(graph))
      return 0;

   // set function
   if (!this -> SetFitFunction(func))
      return 0;

   // perform marginalization
   this -> MarginalizeAll();

   // maximize posterior probability, using the best-fit values close
   // to the global maximum from the MCMC
   this -> FindModeMinuit( this -> GetBestFitParameters(), -1);

   // calculate p-value from the chi2 probability
   // this is only valid for a product of gaussiang which is the case for
   // the BCGraphFitter
   this -> GetPvalueFromChi2(this -> GetBestFitParameters(), 3);

   // print summary to screen
   this -> PrintShortFitSummary();

   return 1;
}

int BCGraphFitter::Fit

(

)

[inline]

Performs the fit. The graph and the function has to beset beforehand.

Returns:

An error code.

Definition at line 117 of file BCGraphFitter.h.

         { return this -> Fit(fGraph, fFitFunction); };

double BCGraphFitter::FitFunction	(	std::vector< double >	x,
		std::vector< double >	parameters
	)			[virtual]

Returns the value of the 1D fit function for a given set of parameters at a given x.

Parameters:

	x	point to calculate the function value at
	parameters	parameters of the function

Reimplemented from BCIntegrate.

Definition at line 230 of file BCGraphFitter.cxx.

{
   // set the parameters of the function
   fFitFunction -> SetParameters(&params[0]);

   return fFitFunction -> Eval(x[0]);
}

TGraph* BCGraphFitter::GetErrorBand

(

)

[inline]

Returns:

pointer to the error band

Definition at line 72 of file BCGraphFitter.h.

         { return fErrorBand; };

TF1* BCGraphFitter::GetFitFunction

(

)

[inline]

Returns:

pointer to TF1

Definition at line 67 of file BCGraphFitter.h.

         { return fFitFunction; };

TGraphErrors* BCGraphFitter::GetGraph

(

)

[inline]

Returns:

pointer to TGraphErrors

Definition at line 62 of file BCGraphFitter.h.

         { return fGraph; };

TGraph* BCGraphFitter::GetGraphFitFunction

(

)

[inline]

Returns:

pointer to a graph for the fit function

Definition at line 77 of file BCGraphFitter.h.

         { return fGraphFitFunction; };

double BCGraphFitter::LogAPrioriProbability

(

std::vector< double >

parameters

)

[virtual]

The log of the prior probability. It is set to be flat in all parameters.

Parameters:

parameters

vector containing the parameter values

Reimplemented from BCModel.

Definition at line 184 of file BCGraphFitter.cxx.

{
   // using flat probability in all parameters
   double logprob = 0.;
   for(unsigned int i=0; i < this -> GetNParameters(); i++)
      logprob -= log(this -> GetParameter(i) -> GetRangeWidth());

   return logprob;
}

double BCGraphFitter::LogLikelihood

(

std::vector< double >

parameters

)

[virtual]

The log of the conditional probability.

Parameters:

parameters

vector containing the parameter values

Reimplemented from BCModel.

Definition at line 196 of file BCGraphFitter.cxx.

{
   // initialize probability
   double logl = 0.;

   // set the parameters of the function
   // passing the pointer to first element of the vector is
   // not completely safe as there might be an implementation where
   // the vector elements are not stored consecutively in memory.
   // however it is much faster than copying the contents, especially
   // for large number of parameters
   fFitFunction -> SetParameters(&params[0]);

   // loop over all data points
   for (int i = 0; i < this -> GetNDataPoints(); i++)
   {
      std::vector <double> x = GetDataPoint(i) -> GetValues();

      // her we ignore the errors on x even when they're available
      // i.e. we treat them just as the region specifiers
      double y = x[1];
      double yerr = x[3];
      double yexp = this -> FitFunction(x,params);

      // calculate log of probability assuming
      // a Gaussian distribution for each point
      logl += BCMath::LogGaus(y, yexp, yerr, true);
   }

   return logl;
}

int BCGraphFitter::SetFitFunction

(

TF1 *

func

)

Parameters:

func

pointer to TF1 object

Definition at line 139 of file BCGraphFitter.cxx.

{
   if(!func)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetFitFunction() : TF1 not created.");
      return 0;
   }

   // get the new number of parameters
   int npar = func -> GetNpar();
   if(!npar)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetFitFunction() : TF1 has zero parameters. Not able to fit.");
      return 0;
   }

   // set the function
   fFitFunction = func;

   // update the model name to contain the function name
   this -> SetName(TString::Format("GraphFitter with %s",fFitFunction->GetName()));

   // reset parameters
   fParameterSet -> clear();

   // add parameters
   for (int i = 0; i < npar; ++i)
   {
      double xmin;
      double xmax;
      fFitFunction -> GetParLimits(i, xmin, xmax);

      this -> AddParameter(fFitFunction->GetParName(i), xmin, xmax);
   }

   return this -> GetNParameters();
}

int BCGraphFitter::SetGraph

(

TGraphErrors *

graph

)

Parameters:

graph

pointer to TGraphErrors object

Definition at line 56 of file BCGraphFitter.cxx.

{
   if(!graph)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetGraph() : TGraphErrors not created.");
      return 0;
   }

   int npoints = graph -> GetN();
   if(!npoints)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetGraph() : TGraphErrors is empty.");
      return 0;
   }
   else if(npoints==1)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetGraph() : TGraphErrors has only one point. Not able to fit.");
      return 0;
   }
   else if(npoints==2)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetGraph() : TGraphErrors has only two points. Fit has no meaning.");
      return 0;
   }

   fGraph = graph;

   double * x = fGraph -> GetX();
   double * y = fGraph -> GetY();
   double * ex = fGraph -> GetEX();
   double * ey = fGraph -> GetEY();

   if(!ey)
   {
      BCLog::Out(BCLog::error,BCLog::error,"BCGraphFitter::SetGraph() : TGraphErrors has no errors set on Y. Not able to fit.");
      return 0;
   }

   BCDataSet * ds = new BCDataSet();

   // fill the dataset
   // find x and y boundaries for the error band calculation
   double xmin=x[0];
   double xmax=x[0];
   double ymin=y[0];
   double ymax=y[0];
   for (int i = 0; i < npoints; ++i)
   {
      // if x errors are not set, set them to zero
      double errx = ex ? ex[i] : 0.;

      // create the data point
      BCDataPoint * dp = new BCDataPoint(4);
      dp -> SetValue(0, x[i]);
      dp -> SetValue(1, y[i]);
      dp -> SetValue(2, errx);
      dp -> SetValue(3, ey[i]);
      ds -> AddDataPoint(dp);

      if(x[i]-errx < xmin)
         xmin = x[i]-errx;
      else if(x[i]+errx > xmax)
         xmax = x[i]+errx;

      if(y[i] - 5.*ey[i] < ymin)
         ymin = y[i] - 5.*ey[i];
      else if(y[i] + 5.*ey[i] > ymax)
         ymax = y[i] + 5.*ey[i];
   }

   this -> SetDataSet(ds);

   // set boundaries for the error band calculation
   this -> SetDataBoundaries(0, xmin, xmax);
   this -> SetDataBoundaries(1, ymin, ymax);

   this -> SetFitFunctionIndices(0, 1);

   return this -> GetNDataPoints();
}

---

Member Data Documentation

TGraph* BCGraphFitter::fErrorBand [private]

Pointer to the error band (for legend)

Definition at line 145 of file BCGraphFitter.h.

TF1* BCGraphFitter::fFitFunction [private]

The fit function

Definition at line 141 of file BCGraphFitter.h.

TGraphErrors* BCGraphFitter::fGraph [private]

The graph containing the data.

Definition at line 137 of file BCGraphFitter.h.

TGraph* BCGraphFitter::fGraphFitFunction [private]

Pointer to a graph for displaying the fit function

Definition at line 149 of file BCGraphFitter.h.