Uso de ROOT

{
   TCanvas *c1 = new TCanvas("c1","A Simple Graph Example",200,10,700,500);
   Double_t x[100], y[100];
   Int_t n = 20;
   for (Int_t i=0;i<n;i++) {
     x[i] = i*0.1;
     y[i] = 10*sin(x[i]+0.2);
   }
   gr = new TGraph(n,x,y);
   gr->Draw("AC*");
   return c1;
}

TF1 *fa2 = new TF1("fa2","TMath::DiLog(x)",0,10); 
  fa2->Draw();

Double_t myFunc(x) { return x+sin(x); } 

TF1 *fa3 = new TF1("fa3","myFunc(x)",-3,5); 
fa3->Draw();

TF1 *fa = new TF1("fa","[0]*x*sin([1]*x)",-3,3); 

fa->SetParameter(0,value_first_parameter);
fa->SetParameter(1,value_second_parameter);

TF1 *fb2 = new TF1("fa3","TMath::Landau(x,[0],[1],0)",-5,10);
fb2->SetParameters(0.2,1.3);
fb2->Draw();

// Macro myfunc.C
Double_t myfunction(Double_t *x, Double_t *par)
{
   Float_t xx =x[0];
   Double_t f = TMath::Abs(par[0]*sin(par[1]*xx)/xx);
   return f;
}
void myfunc()
{
   TF1 *f1 = new TF1("myfunc",myfunction,0,10,2);
   f1->SetParameters(2,1);
   f1->SetParNames("constant","coefficient");
   f1->Draw();
}
void myfit()
{
   TH1F *h1=new TH1F("h1","test",100,0,10);
   h1->FillRandom("myfunc",20000);
   TF1 *f1=gROOT->GetFunction("myfunc");
   f1->SetParameters(800,1);
   h1->Fit("myfunc");
}

Root > .L myfunc.C
Root > myfunc();
Root > myfit();