#include "Riostream.h"
#include "TMath.h"
#include "TMinuit.h"
#include <stdlib.h>
#include <sstream>

using namespace std;


Double32_t p0,p1,p1err, p0err;
Double32_t x[16] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
Double32_t y[16],z[16],x1[120],error[16];


Double_t func(Double32_t x, Double32_t *par)
{
 Double_t arg = 0;
   arg = (x*par[1])+par[0];
   Double_t value = TMath::Exp(arg);
 return value;
}


void fcn(Int_t &npar, Double_t *gin, Double_t &f, Double_t *par, Int_t iflag)
{
   const Int_t nbins = 8;
   Int_t i;
   Double_t chisq = 0;
   Double_t delta;
   for (i=3;i<nbins; i++) 
   {
     delta  = (y[i]-func(x[i],par))/error[i];
     chisq += delta*delta;
   }
   f = chisq;
}


void myfit()

{
TMinuit *gMinuit = new TMinuit(2);
gMinuit->SetFCN(fcn);
Double_t arglist[10];
   Int_t ierflg = 0;
   arglist[0] = 1;
gMinuit->mnexcm("SET ERR", arglist ,1,ierflg);

gMinuit->mnparm(0, "p0", 0.5, 0.01, 0,0,ierflg);
gMinuit->mnparm(1, "p1", -0.05, 0.001, 0,0.0,ierflg);


string nume="fin.out";
Int_t m=0,k,d;
ifstream in;
in.open(nume.c_str());
cout<<endl<<nume.c_str()<<endl;
double a;
in>>a;
for (i=0; i<16; i++) 
{
y[i]=0;
in>>y[i]>>error[i];
cout<<" "<<y[i]<<" "<<error[i];
}
arglist[0] = 500;
arglist[1]=1.;
gMinuit->mnexcm("MIGRAD", arglist ,2,ierflg);
Double_t amin,edm,errdef;
Int_t nvpar,nparx,icstat;
gMinuit->mnstat(amin,edm,errdef,nvpar,nparx,icstat);
gMinuit->mnprin(3,amin);
cout<<"aaaaa  "<<fcn;
gMinuit->mnprin(3,amin);
gMinuit->GetParameter(1,p1,p1err);
gMinuit->GetParameter(0,p0,p0err);

stringstream out;
string nume="out.out";
ofstream file;
file.open(nume.c_str(),ios::app);
file<<setiosflags(ios::fixed) << setprecision(12)<<a<<"     "<<-p1<<"    "<<p0<<"    "<<amin<<endl;
file.close();


}