void Ylm(const Int_t l = 3,const Int_t m = 2){

   const Double_t pi = TMath::Pi();

   TF2 *Ylm = new TF2("Ylm","[0]*ROOT::Math::assoc_legendre([1],[2],cos(x))*cos([2]*y)");

   Ylm->SetRange(0,0,pi,2*pi);

   Double_t n = sqrt(((2*l+1)/4*pi)*(TMath::Factorial(l-m)/TMath::Factorial(l+m)));
   
   Ylm->SetParameter(0,n);
   Ylm->SetParameter(1,l);
   Ylm->SetParameter(2,m);

   Ylm->Draw("surf1 sph");
}