approx.C

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/// \file
/// \ingroup tutorial_graphs
/// \notebook -js
/// Macro to test interpolation function Approx
///
/// \macro_image
/// \macro_code
///
/// \author Christian Stratowa, Vienna, Austria.
 
TCanvas *vC1;
TGraph *grxy, *grin, *grout;
 
void DrawSmooth(Int_t pad, const char *title, const char *xt, const char *yt)
{
   vC1->cd(pad);
   TH1F *vFrame = gPad->DrawFrame(0, 0, 15, 150);
   vFrame->SetTitle(title);
   vFrame->SetTitleSize(0.2);
   vFrame->SetXTitle(xt);
   vFrame->SetYTitle(yt);
   grxy->SetMarkerColor(kBlue);
   grxy->SetMarkerStyle(21);
   grxy->SetMarkerSize(0.5);
   grxy->Draw("P");
   grin->SetMarkerColor(kRed);
   grin->SetMarkerStyle(5);
   grin->SetMarkerSize(0.7);
   grin->Draw("P");
   grout->DrawClone("LP");
}
 
void approx()
{
   // Test data (square)
   Int_t n = 11;
   Double_t x[] = {1, 2, 3, 4, 5, 6, 6, 6, 8, 9, 10};
   Double_t y[] = {1, 4, 9, 16, 25, 25, 36, 49, 64, 81, 100};
   grxy = new TGraph(n, x, y);
 
   // X values, for which y values should be interpolated
   Int_t nout = 14;
   Double_t xout[] = {1.2, 1.7, 2.5, 3.2, 4.4, 5.2, 5.7, 6.5, 7.6, 8.3, 9.7, 10.4, 11.3, 13};
 
   // Create Canvas
   vC1 = new TCanvas("vC1", "square", 200, 10, 700, 700);
   vC1->Divide(2, 2);
 
   // Initialize graph with data
   grin = new TGraph(n, x, y);
   // Interpolate at equidistant points (use mean for tied x-values)
   TGraphSmooth *gs = new TGraphSmooth("normal");
   grout = gs->Approx(grin, "linear");
   DrawSmooth(1, "Approx: ties = mean", "X-axis", "Y-axis");
 
   // Re-initialize graph with data
   // (since graph points were set to unique vales)
   grin = new TGraph(n, x, y);
   // Interpolate at given points xout
   grout = gs->Approx(grin, "linear", 14, xout, 0, 130);
   DrawSmooth(2, "Approx: ties = mean", "", "");
 
   // Print output variables for given values xout
   Int_t vNout = grout->GetN();
   Double_t vXout, vYout;
   for (Int_t k = 0; k < vNout; k++) {
      grout->GetPoint(k, vXout, vYout);
      cout << "k= " << k << "  vXout[k]= " << vXout << "  vYout[k]= " << vYout << endl;
   }
 
   // Re-initialize graph with data
   grin = new TGraph(n, x, y);
   // Interpolate at equidistant points (use min for tied x-values)
   //   _grout = gs->Approx(grin,"linear", 50, 0, 0, 0, 1, 0, "min");_
   grout = gs->Approx(grin, "constant", 50, 0, 0, 0, 1, 0.5, "min");
   DrawSmooth(3, "Approx: ties = min", "", "");
 
   // Re-initialize graph with data
   grin = new TGraph(n, x, y);
   // Interpolate at equidistant points (use max for tied x-values)
   grout = gs->Approx(grin, "linear", 14, xout, 0, 0, 2, 0, "max");
   DrawSmooth(4, "Approx: ties = max", "", "");
 
   // Cleanup
   delete gs;
}