splines.C: examples of use of the spline classes

void splines (Int_t np=23, Double_t a=-0.5, Double_t b=31)
{
  // examples of use of the spline classes
  //Author: Federico Carminati
   
  // array of points
  Double_t *xx=0, *yy=0;
  TSpline3 *spline3=0;
  TSpline5 *spline5=0;
  TLine *line5, *line3;
  TText *text5, *text3, *textn;
  char text[20];
  const Double_t power=0.75;

  // Define the original function
  TF1 *f=new TF1("f","sin(x)*sin(x/10)",
		 a-0.05*(b-a),b+0.05*(b-a));
  // Draw function
  f->Draw("lc");

    // Create text and legend
  Float_t xx1, yy1, xx2, yy2, dx, dy;
  gPad->Update();
  gPad->GetRangeAxis(xx1,yy1,xx2,yy2);
  dx = xx2-xx1;
  dy = yy2-yy1;
  line5=new TLine(xx1+dx*0.3,yy1+dy*1.02,
		  xx1+dx*0.38,yy1+dy*1.02);
  line5->SetLineColor(kRed);
  line5->SetLineWidth(2);
  text5 = new TText(xx1+dx*0.4,
		    yy1+dy*1.03,"quintic spline");
  text5->SetTextAlign(12);
  text5->SetTextSize(0.04);
  line3=new TLine(xx1+dx*0.67,yy1+dy*1.02,
		  xx1+dx*0.75,yy1+dy*1.02);
  line3->SetLineColor(kGreen);
  line3->SetLineWidth(2);
  text3 = new TText(xx1+dx*0.77,
		    yy1+dy*1.03,"third spline");
  text3->SetTextAlign(12);
  text3->SetTextSize(0.04);
  textn = new TText(xx1+dx*0.8,yy1+dy*0.91," ");
  textn->SetTextAlign(12);
  textn->SetTextSize(0.04);
  textn->Draw();

  // Draw legenda
  line5->Draw();
  text5->Draw();
  line3->Draw();
  text3->Draw();

  for(Int_t nnp=2; nnp<=np; ++nnp) {

    // Calculate the knots
    if(xx) delete[] xx;
    xx = new Double_t[nnp];
    if(yy) delete[] yy;
    yy = new Double_t[nnp];
    for (Int_t i=0; i<nnp; ++i) {
      xx[i]=a+(b-a)*TMath::Power(i/Double_t (nnp-1),power);
      yy[i]=f->Eval(xx[i]);
    }

    // Evaluate fifth spline coefficients
    Double_t eps=(b-a)*1.e-5;
    if(spline5) delete spline5;
    spline5 = new TSpline5("Test",xx,f,nnp,"b1e1b2e2",
			   f->Derivative(a),f->Derivative(b),
			   (f->Derivative(a+eps)-f->Derivative(a))/eps,
			   (f->Derivative(b)-f->Derivative(b-eps))/eps);

    spline5->SetLineColor(kRed);
    spline5->SetLineWidth(3);

    // Draw the quintic spline
    spline5->Draw("lcsame");

    // Evaluate third spline coefficients
    if(spline3) delete spline3;
    spline3 = new TSpline3("Test",xx,yy,nnp,"b1e1",
			   f->Derivative(a),f->Derivative(b));

    spline3->SetLineColor(kGreen);
    spline3->SetLineWidth(3);
    spline3->SetMarkerColor(kBlue);
    spline3->SetMarkerStyle(20);
    spline3->SetMarkerSize(1.5);

    // Draw the third spline
    spline3->Draw("lcpsame");

    sprintf(text,"%3d knots",nnp);
    textn->SetTitle(text);
    gPad->Update();

    //
    gSystem->Sleep(500);
  }
}