// Double_t myfunc(Double_t *x, Double_t *p) {
Double_t myfunc(Double_t x[], Double_t p[]) {
  return p[0] * sin( (x[0]-p[2]) ) / (x[0]-p[2])   +  p[1] ;
  // p[0] : κλίμακα
  // p[1] : μετατόπιση στο y
  // p[2] : μετατόπιση στο x
}

void sinc() {

  int np=301;
  double  x[np];
  double  y[np];
  double ex[np];
  double ey[np];

  // x: -10 .. 10
  double x1=-10;
  double x2= 10;

  // y: sin(x)/x +- gaussian noise

  TTimeStamp *t = new TTimeStamp();
  gRandom->SetSeed(t->GetNanoSec());

  for (int i=0 ; i<np ; i++) {
    x[i]  = x1 + (x2-x1) * i/(np-1.) ;
    y[i]  = 0.02*gRandom->Gaus(0,0.5)   -3.2   +   10* ( (x[i]-1.5)==0 ? 1 : sin(x[i]-1.5)/(x[i]-1.5) ) ;
    ex[i] = (x2-x1)/(np-1)/3.;
    ey[i] = 0.02+fabs(0.01*y[i]);
  }


  TCanvas *c1 = new TCanvas("canvas11","sinc data simulation and fit",1200,800);
  gStyle->SetOptFit(1);
  c1->SetGridx();
  c1->SetGridy();
  c1->Draw();


  TGraphErrors *g = new TGraphErrors(np,x,y,ex,ey);
  g->SetName("g");
  g->SetTitle("fitted data");
  g->SetMarkerColor(8);
  g->SetMarkerStyle(20);
  g->SetMarkerSize(1);
  g->Draw("AP");

  TF1 *fitfunc = new TF1( "fname", myfunc, -10, 10, 3);

  fitfunc->SetLineWidth(2);

  fitfunc->SetParameter(0, 0.8);
  fitfunc->SetParameter(1, 0.5);
  fitfunc->SetParameter(2, 0.5);

  fitfunc->SetParLimits(0,   0,   10);
  fitfunc->SetParLimits(1, -100, 100);
  fitfunc->SetParLimits(2,  -10,  10);

  g->Fit(fitfunc);
}