Trouble with using TF1

From: Matthew Martin (msmartin@fnal.gov)
Date: Thu Oct 21 1999 - 23:59:20 MEST 

Hi Rooters,
	I've been trying to get the following macro to work for sometime
now with zero success. 





Double_t Open_fcn(Double_t *x, Double_t *par){
  Float_t xx =x[0];
  Double_t phi_mass=1.02;
  Double_t k_mass=493.68;
  Double_t Ek_CM,Pk_CM;
  Double_t beta;
  Double_t gamma=5.0;
  Ek_CM=phi_mass/2.0;
  Pk_CM=TMath::Sqrt( (Ek_CM*Ek_CM)-(k_mass*k_mass) );
  beta=TMath::Sqrt( 1.0-TMath::Power( gamma,-2.0 )  );
  Double_t
f=(TMath::ATan(Pk_CM*TMath::Sin(xx)/(gamma*(Pk_CM*TMath::Cos(xx)+beta*Ek_CM))
) +
TMath::ATan(Pk_CM*TMath::Sin(xx)/(gamma*(Pk_CM*TMath::Cos(xx)-beta*Ek_CM))
));
  return f;
}//Open_fcn

   
void draw_it()
{
 TF1* open_dist = new TF1("open_dist",Open_fcn,0.0,3.14159,0);
 TCanvas* c1 = new TCanvas("c1","Opening angle dists",10,10,1200,950);
 c1->cd();
 open_dist->Draw();
}





I load it into memory, and then execute the
draw_it() function, and I get the following error:

Error in <TGaxis::PaintAxis>: wmin (-0.000000) == wmax (-0.000000)
root [2] Error in <TGaxis::PaintAxis>: wmin (-0.000000) == wmax
(-0.000000)


how can I get it to work?

cheers

Mat

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