motorcycle.C File Reference

Detailed Description

Macro to test scatterplot smoothers: ksmooth, lowess, supsmu as described in:

 Modern Applied Statistics with S-Plus, 3rd Edition
 W.N. Venables and B.D. Ripley
 Chapter 9: Smooth Regression, Figure 9.1

Example is a set of data on 133 observations of acceleration against time for a simulated motorcycle accident, taken from Silverman (1985).

 
#include "TString.h"
#include "TInterpreter.h"
#include <fstream>
#include "TH1.h"
#include "TGraphSmooth.h"
#include "TCanvas.h"
#include "TSystem.h"
 
TCanvas *vC1;
TGraph *grin, *grout;
 
void DrawSmooth(Int_t pad, const char *title, const char *xt, const char *yt)
{
   vC1->cd(pad);
   TH1F *vFrame = gPad->DrawFrame(0, -130, 60, 70);
   vFrame->SetTitle(title);
   vFrame->SetTitleSize(0.2);
   vFrame->SetXTitle(xt);
   vFrame->SetYTitle(yt);
   grin->Draw("P");
   grout->DrawClone("LPX");
}
 
void motorcycle()
{
   // data taken from R library MASS: mcycle.txt
   TString dir = gROOT->GetTutorialDir();
   dir.Append("/visualisation/graphs/");
   dir.ReplaceAll("/./", "/");
 
   // read file and add to fit object
   Double_t *x = new Double_t[133];
   Double_t *y = new Double_t[133];
   Double_t vX, vY;
   Int_t vNData = 0;
   ifstream vInput;
   vInput.open(Form("%smotorcycle.dat", dir.Data()));
   while (1) {
      vInput >> vX >> vY;
      if (!vInput.good())
         break;
      x[vNData] = vX;
      y[vNData] = vY;
      vNData++;
   } // while
   vInput.close();
   grin = new TGraph(vNData, x, y);
 
   // draw graph
   vC1 = new TCanvas("vC1", "Smooth Regression", 200, 10, 900, 700);
   vC1->Divide(2, 3);
 
   // Kernel Smoother
   // create new kernel smoother and smooth data with bandwidth = 2.0
   TGraphSmooth *gs = new TGraphSmooth("normal");
   grout = gs->SmoothKern(grin, "normal", 2.0);
   DrawSmooth(1, "Kernel Smoother: bandwidth = 2.0", "times", "accel");
 
   // redraw ksmooth with bandwidth = 5.0
   grout = gs->SmoothKern(grin, "normal", 5.0);
   DrawSmooth(2, "Kernel Smoother: bandwidth = 5.0", "", "");
 
   // Lowess Smoother
   // create new lowess smoother and smooth data with fraction f = 2/3
   grout = gs->SmoothLowess(grin, "", 0.67);
   DrawSmooth(3, "Lowess: f = 2/3", "", "");
 
   // redraw lowess with fraction f = 0.2
   grout = gs->SmoothLowess(grin, "", 0.2);
   DrawSmooth(4, "Lowess: f = 0.2", "", "");
 
   // Super Smoother
   // create new super smoother and smooth data with default bass = 0 and span = 0
   grout = gs->SmoothSuper(grin, "", 0, 0);
   DrawSmooth(5, "Super Smoother: bass = 0", "", "");
 
   // redraw supsmu with bass = 3 (smoother curve)
   grout = gs->SmoothSuper(grin, "", 3);
   DrawSmooth(6, "Super Smoother: bass = 3", "", "");
 
   // cleanup
   delete[] x;
   delete[] y;
   delete gs;
}

Author

Christian Stratowa, Vienna, Austria

Definition in file motorcycle.C.