TCanvas *c1=new TCanvas("c1", "TMath::BetaDist",600,800);
c1->Divide(1, 2);
TVirtualPad *pad1 = c1->cd(1);
pad1->SetGrid();
TF1 *fbeta = new TF1("fbeta", "TMath::BetaDist(x, [0], [1])", 0, 1);
fbeta->SetParameters(0.5, 0.5);
TF1 *f1 = fbeta->DrawCopy();
f1->SetLineColor(kRed);
f1->SetLineWidth(1);
fbeta->SetParameters(0.5, 2);
TF1 *f2 = fbeta->DrawCopy("same");
f2->SetLineColor(kGreen);
f2->SetLineWidth(1);
fbeta->SetParameters(2, 0.5);
TF1 *f3 = fbeta->DrawCopy("same");
f3->SetLineColor(kBlue);
f3->SetLineWidth(1);
fbeta->SetParameters(2, 2);
TF1 *f4 = fbeta->DrawCopy("same");
f4->SetLineColor(kMagenta);
f4->SetLineWidth(1);
TLegend *legend1 = new TLegend(.5,.7,.8,.9);
legend1->AddEntry(f1,"p=0.5  q=0.5","l");
legend1->AddEntry(f2,"p=0.5  q=2","l");
legend1->AddEntry(f3,"p=2    q=0.5","l");
legend1->AddEntry(f4,"p=2    q=2","l");
legend1->Draw();

TVirtualPad *pad2 = c1->cd(2);
pad2->SetGrid();
TF1 *fbetai=new TF1("fbetai", "TMath::BetaDistI(x, [0], [1])", 0, 1);
fbetai->SetParameters(0.5, 0.5);
TF1 *g1=fbetai->DrawCopy();
g1->SetLineColor(kRed);
g1->SetLineWidth(1);
fbetai->SetParameters(0.5, 2);
TF1 *g2=fbetai->DrawCopy("same");
g2->SetLineColor(kGreen);
g2->SetLineWidth(1);
fbetai->SetParameters(2, 0.5);
TF1 *g3=fbetai->DrawCopy("same");
g3->SetLineColor(kBlue);
g3->SetLineWidth(1);
fbetai->SetParameters(2, 2);
TF1 *g4=fbetai->DrawCopy("same");
g4->SetLineColor(kMagenta);
g4->SetLineWidth(1);

TLegend *legend2 = new TLegend(.7,.15,0.9,.35);
legend2->AddEntry(f1,"p=0.5  q=0.5","l");
legend2->AddEntry(f2,"p=0.5  q=2","l");
legend2->AddEntry(f3,"p=2    q=0.5","l");
legend2->AddEntry(f4,"p=2    q=2","l");
legend2->Draw();
c1->cd();

gROOT->GetListOfCanvases()->Draw()