#include "TMinuit.h"
#include "events.h"
#include <TStyle.h>
#include <TCanvas.h>
#include <iostream>
#include <TH1F.h>
#include <TLorentzVector.h>
#include "TRandom.h"
#include <math.h>

Float_t x[100],y[100],errory[100];

//______________________________________________________________________________
Double_t func(float x,Double_t *par)
{
  Double_t value=par[0] * exp( -x/par[1]);
  return value;
}

//______________________________________________________________________________
void fcn(Int_t &npar, Double_t *gin, Double_t &f, Double_t *par, Int_t iflag)
{
  const Int_t nbins = 100;
  Int_t i;

  //calculate chisquare
  Double_t chisq = 0;
  Double_t delta;
  for (i=0;i<nbins; i++) {
    delta  = (y[i]-func(x[i],par))/errory[i];
    chisq += delta*delta;
  }
  f = chisq;
}

//______________________________________________________________________________
void Ifit()
{
  TH1F * ExpFall = new TH1F("ExpFall", "", 100, -0.5, 99.5);
  
  for(int i=0; i<100; i++){
    ExpFall->SetBinContent(i+1, exp(-i));
    ExpFall->SetBinError( i+1,   0.01);
    x[i] = i;
    y[i] = exp(-i);
    errory[i] = 0.01;
  }

  ExpFall->Draw();

//  TMinuit *gMinuit = new TMinuit(2);  //initialize TMinuit with a maximum of 2 params
//  gMinuit->SetFCN(fcn);
//
//  Double_t arglist[10];
//  Int_t ierflg = 0;
//
//  arglist[0] = 1;
//  gMinuit->mnexcm("SET ERR", arglist ,1,ierflg);
//
//  // Set starting values and step sizes for parameters
//  static Double_t vstart[2] = {3, 2};
//  static Double_t step[2] = {0.001, 0.001};
//  gMinuit->mnparm(0, "norm", vstart[0], step[0], 0, 2,ierflg);
//  gMinuit->mnparm(1, "decay", vstart[1], step[1], 0, 2,ierflg);
//
//  // Now ready for minimization step
//  arglist[0] = 1000;
//  arglist[1] = 1.;
//  gMinuit->mnexcm("MIGRAD", arglist ,2,ierflg);
//
//  // Print results
//  Double_t amin,edm,errdef;
//  Int_t nvpar,nparx,icstat;
//  gMinuit->mnstat(amin,edm,errdef,nvpar,nparx,icstat);


}