hist104_TH2Poly_fibonacci.C File Reference

Detailed Description

A TH2Poly build with Fibonacci numbers.

In mathematics, the Fibonacci sequence is a suite of integer in which every number is the sum of the two preceding one.

The first 10 Fibonacci numbers are:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...

This tutorial computes Fibonacci numbers and uses them to build a TH2Poly producing the "Fibonacci spiral" created by drawing circular arcs connecting the opposite corners of squares in the Fibonacci tiling.

 
void Arc(int n, double a, double r, double *px, double *py);
void AddFibonacciBin(TH2Poly *h2pf, double N);
 
void hist104_TH2Poly_fibonacci(int N = 7)
{
   // N = number of Fibonacci numbers > 1
 
   TCanvas *C = new TCanvas("C", "C", 800, 600);
   C->SetFrameLineWidth(0);
 
   TH2Poly *h2pf = new TH2Poly(); // TH2Poly containing Fibonacci bins.
   h2pf->SetTitle(Form("The first %d Fibonacci numbers", N));
   h2pf->SetMarkerColor(kRed - 2);
   h2pf->SetStats(0);
 
   double f0 = 0.;
   double f1 = 1.;
   double ft;
 
   AddFibonacciBin(h2pf, f1);
 
   for (int i = 0; i <= N; i++) {
      ft = f1;
      f1 = f0 + f1;
      f0 = ft;
      AddFibonacciBin(h2pf, f1);
   }
 
   h2pf->Draw("A COL L TEXT");
}
 
void Arc(int n, double a, double r, double *px, double *py)
{
   // Add points on a arc of circle from point 2 to n-2
 
   double da = TMath::Pi() / (2 * (n - 2)); // Angle delta
 
   for (int i = 2; i <= n - 2; i++) {
      a = a + da;
      px[i] = r * TMath::Cos(a) + px[0];
      py[i] = r * TMath::Sin(a) + py[0];
   }
}
 
void AddFibonacciBin(TH2Poly *h2pf, double N)
{
   // Add to h2pf the bin corresponding to the Fibonacci number N
 
   double X1 = 0.; //
   double Y1 = 0.; // Current Fibonacci
   double X2 = 1.; // square position.
   double Y2 = 1.; //
 
   static int MoveId = 0;
 
   static double T = 1.; // Current Top limit of the bins
   static double B = 0.; // Current Bottom limit of the bins
   static double L = 0.; // Current Left limit of the bins
   static double R = 1.; // Current Right limit of the bins
 
   const int NP = 50; // Number of point to build the current bin
   double px[NP];     // Bin's X positions
   double py[NP];     // Bin's Y positions
 
   double pi2 = TMath::Pi() / 2;
 
   switch (MoveId) {
   case 1:
      R = R + N;
      X2 = R;
      Y2 = T;
      X1 = X2 - N;
      Y1 = Y2 - N;
      px[0] = X1;
      py[0] = Y2;
      px[1] = X1;
      py[1] = Y1;
      px[NP - 1] = X2;
      py[NP - 1] = Y2;
      Arc(NP, 3 * pi2, (double)N, px, py);
      break;
 
   case 2:
      T = T + N;
      X2 = R;
      Y2 = T;
      X1 = X2 - N;
      Y1 = Y2 - N;
      px[0] = X1;
      py[0] = Y1;
      px[1] = X2;
      py[1] = Y1;
      px[NP - 1] = X1;
      py[NP - 1] = Y2;
      Arc(NP, 0., (double)N, px, py);
      break;
 
   case 3:
      L = L - N;
      X1 = L;
      Y1 = B;
      X2 = X1 + N;
      Y2 = Y1 + N;
      px[0] = X2;
      py[0] = Y1;
      px[1] = X2;
      py[1] = Y2;
      px[NP - 1] = X1;
      py[NP - 1] = Y1;
      Arc(NP, pi2, (double)N, px, py);
      break;
 
   case 4:
      B = B - N;
      X1 = L;
      Y1 = B;
      X2 = X1 + N;
      Y2 = Y1 + N;
      px[0] = X2;
      py[0] = Y2;
      px[1] = X1;
      py[1] = Y2;
      px[NP - 1] = X2;
      py[NP - 1] = Y1;
      Arc(NP, 2 * pi2, (double)N, px, py);
      break;
   }
 
   if (MoveId == 0)
      h2pf->AddBin(X1, Y1, X2, Y2); // First bin is a square
   else
      h2pf->AddBin(NP, px, py); // Other bins have an arc of circle
 
   h2pf->Fill((X1 + X2) / 2.5, (Y1 + Y2) / 2.5, N);
 
   MoveId++;
   if (MoveId == 5)
      MoveId = 1;
}

Date

September 2016

Author

Olivier Couet

Definition in file hist104_TH2Poly_fibonacci.C.