splines_test.C

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/// \file
/// \ingroup tutorial_graphs
/// \notebook
/// Examples of use of the spline classes.
///
/// \macro_image
/// \macro_code
///
/// \author Federico Carminati

void splines_test(Int_t np=23, Double_t a=-0.5, Double_t b=31)
{
   // 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
   Double_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);
   }
}