Double_t Nasser(Double_t *x, Double_t *par)
{
Double_t arg = 0;
arg = exp(107.92 -2.254*pow((x[0]/1e9),-1) +34.19*pow((x[0]/1e9),-1/3) -167.81*pow((x[0]/1e9),1/3)
	+6.867*(x[0]/1e9) -0.2649*pow((x[0]/1e9),5/3) +82.15*log(x[0]/1e9));
return arg;
}

void Nasser()
{
TF1 *Nass= new TF1("Nass","exp(107.92 -2.254/(x/1e9) +34.19*pow((x/1e9),-1/3) -167.81*pow((x/1e9),1/3) +6.867*(x/1e9) -0.2649*pow((x/1e9),5/3) +82.15*log((x/1e9)))",0.1E9,6E9) ; 
Nass->Draw();

TF1 *Gfit = new TF1("Gfit",Nasser,0.1E9,6E9,0);
Gfit->SetLineColor(3);
Gfit->Draw("SAME");
}