void func(Int_t& npar, Double_t* gin, Double_t& f, Double_t* par, Int_t iflag)
{
  printf("NPAR = %d\n",npar);
  for (Int_t i = 0 ; i<npar; i++) gin[i]=1;
  return;
}

doit()
{
  if (!gMinuit)
  {
    gMinuit = new TMinuit(3);
    gMinuit->SetFCN(func);

    gMinuit->DefineParameter(0,"a", 0, 0.1, 0, 0);
    gMinuit->DefineParameter(1,"b", 0, 0.1, 0, 0);
    gMinuit->DefineParameter(2,"c", 0, 0.1, 0, 0);
  }

  Double_t arglist[20];
  Int_t ierflg = 0;

  arglist[0] = 3; // 0 means minimal output; -1 is no output
  gMinuit->mnexcm("SET PRINTOUT", arglist,1,ierflg);
  gMinuit->mnexcm("SET GRADIENT 1",0,0,ierflg);

  gMinuit->FixParameter(0);
  gMinuit->mnexcm("SET GRADIENT 1",0,0,ierflg);
}