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Filling and fitting histos

Histograms with Random Numbers from a Function

{
   //
   gROOT->Reset();
   c1 = new TCanvas("c1","The FillRandom example",200,10,700,900);
   c1->SetFillColor(18);

   pad1 = new TPad("pad1","The pad with the function",0.05,0.50,0.95,0.95,21);
   pad2 = new TPad("pad2","The pad with the histogram",0.05,0.05,0.95,0.45,21);
   pad1->Draw();
   pad2->Draw();
   pad1->cd();

   gBenchmark->Start("fillrandom");
   //
   // A function (any dimension) or a formula may reference
   // an already defined formula
   //
   form1 = new TFormula("form1","abs(sin(x)/x)");
   sqroot = new TF1("sqroot","x*gaus(0) + [3]*form1",0,10);
   sqroot->SetParameters(10,4,1,20);
   pad1->SetGridx();
   pad1->SetGridy();
   pad1->GetFrame()->SetFillColor(42);
   pad1->GetFrame()->SetBorderMode(-1);
   pad1->GetFrame()->SetBorderSize(5);
   sqroot->SetLineColor(4);
   sqroot->SetLineWidth(6);
   sqroot->Draw();
   lfunction = new TPaveLabel(5,39,9.8,46,"The sqroot function");
   lfunction->SetFillColor(41);
   lfunction->Draw();
   c1->Update();

   //
   // Create a one dimensional histogram (one float per bin)
   // and fill it following the distribution in function sqroot.
   //
   pad2->cd();
   pad2->GetFrame()->SetFillColor(42);
   pad2->GetFrame()->SetBorderMode(-1);
   pad2->GetFrame()->SetBorderSize(5);
   h1f = new TH1F("h1f","Test random numbers",200,0,10);
   h1f->SetFillColor(45);
   h1f->FillRandom("sqroot",10000);
   h1f->Draw();
   c1->Update();
   //
   // Open a ROOT file and save the formula, function and histogram
   //
   TFile myfile("fillrandom.root","RECREATE");
   form1->Write();
   sqroot->Write();
   h1f->Write();
   myfile.Close();
   gBenchmark->Show("fillrandom");
}

A Simple Fitting Example

{
   //
   gROOT->Reset();
   c1 = new TCanvas("c1","The Fit Canvas",200,10,700,500);
   c1->SetGridx();
   c1->SetGridy();
   c1->GetFrame()->SetFillColor(21);
   c1->GetFrame()->SetBorderMode(-1);
   c1->GetFrame()->SetBorderSize(5);

   gBenchmark->Start("fit1");
   //
   // We connect the ROOT file generated in a previous tutorial
   // (see  Filling histograms with random numbers from a function) 
   //
   TFile fill("fillrandom.root");

   //
   // The function "ls()" lists the directory contents of this file
   //
   fill.ls();

   //
   // Get object "sqroot" from the file. Undefined objects are searched
   // for using gROOT->FindObject("xxx"), e.g.:
   // TF1 *sqroot = (TF1*) gROOT.FindObject("sqroot")
   //
   sqroot->Print();

   //
   // Now fit histogram h1f with the function sqroot
   //
   h1f->SetFillColor(45);
   h1f->Fit("sqroot");

   // We now annotate the picture by creating a PaveText object
   // and displaying the list of commands in this macro
   //
   fitlabel = new TPaveText(0.6,0.3,0.9,0.80,"NDC");
   fitlabel->SetTextAlign(12);
   fitlabel->SetFillColor(42);
   fitlabel->ReadFile("fit1_C.C");
   fitlabel->Draw();
   c1->Update();
   gBenchmark->Show("fit1");
}

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