Double_t trace(Double_t *x, Double_t *par)
{
  Double_t value;

    if( x[0] < par[2] )
    {
      value = par[3] * TMath::Exp((x[0] - par[2])/par[1]);
    }
  else
    {
      value = (par[3] - par[5]) * TMath::Exp((par[2] - x[0])/par[0]) + par[5] * TMath::Exp((par[2] - x[0])/par[4]);
    }

  return value;
}