ROOT Tips Tricks

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ROOT Tips Tricks

float_double.C

// Author: Jan Musinsky
// 14/10/2014

#include <TMath.h>

void float_double()
{
  Float_t fmin = TMath::Limits<Float_t>::Min();
  Float_t fmax = TMath::Limits<Float_t>::Max();
  Float_t feps = TMath::Limits<Float_t>::Epsilon();

  Double_t dmin = TMath::Limits<Double_t>::Min();
  Double_t dmax = TMath::Limits<Double_t>::Max();
  Double_t deps = TMath::Limits<Double_t>::Epsilon();

  Float_t  f1 = 1234567890123456789012345.1234567890123456789012345;
  Float_t  f2 = 1234567890123456789012345.0;
  Float_t  f3 = 0.1234567890123456789012345;
  Float_t  fi = 1234567890123456789012345;

  Double_t  d1 = 1234567890123456789012345.1234567890123456789012345;
  Double_t  d2 = 1234567890123456789012345.0;
  Double_t  d3 = 0.1234567890123456789012345;
  Double_t  di = 1234567890123456789012345;

  printf("float  min = %g\n", fmin);
  printf("float  max = %g\n", fmax);
  printf("double min = %g\n", dmin);
  printf("double max = %g\n", dmax);
  printf("float  epsilon = %.60f => %g\n", feps, feps);
  printf("double epsilon = %.60f => %g\n", deps, deps);
  printf("\n\n");
  printf("number    1234567890123456789012345.1234567890123456789012345\n");
  printf("as float  %f => %g\n", f1, f1);
  printf("as double %f => %g\n", d1, d1);
  printf("\n");
  printf("number    1234567890123456789012345.0\n");
  printf("as float  %f => %g\n", f2, f2);
  printf("as double %f => %g\n", d2, d2);
  printf("\n");
  printf("number    0.1234567890123456789012345\n");
  printf("as float  %.60f => %g\n", f3, f3);
  printf("as double %.60f => %g\n", d3, d3);
  printf("\n");
  printf("number    1234567890123456789012345 (no decimal)\n");
  printf("as float  %f => %g\n", fi, fi);
  printf("as double %f => %g\n", di, di);

  Float_t  fbig = 9.123e+22;
  Double_t dbig = 9.123e+22;
  printf("\n");
  printf("number    9.123e+22\n");
  printf("as float  %f => %g\n", fbig, fbig);
  printf("as double %f => %g\n", dbig, dbig);
  Float_t  fbig2 = 9.123e+40;
  Double_t dbig2 = 9.123e+40;
  printf("\n");
  printf("number    9.123e+40\n");
  printf("as float  %f => %g\n", fbig2, fbig2);
  printf("as double %f => %g\n", dbig2, dbig2);
  Float_t  fsmall = 9.123e-10;
  Double_t dsmall = 9.123e-10;
  printf("\n");
  printf("number    9.123e-10\n");
  printf("as float  %.60f => %g\n", fsmall, fsmall);
  printf("as double %.60f => %g\n", dsmall, dsmall);
  Float_t  fsmall2 = 9.123e-50;
  Double_t dsmall2 = 9.123e-50;
  printf("\n");
  printf("number    9.123e-50\n");
  printf("as float  %.60f => %g\n", fsmall2, fsmall2);
  printf("as double %.60f => %g\n", dsmall2, dsmall2);
}

graph_real_time.C

// 2016-11-21

{
  Int_t delay = 500;

  TGraph *g = new TGraph(100);
  g->SetMarkerStyle(8);
  g->Draw("AP");
  gPad->SetGridx();
  gPad->Modified();
  gPad->Update();

  TDatime dt;
  gStyle->SetTimeOffset(dt.Convert());

  for (Int_t i = 0; i < g->GetN(); i++) {
    dt.Set();
    g->SetPoint(i, dt.Convert() - gStyle->GetTimeOffset(), i%5);
    Printf("%f",   dt.Convert() - gStyle->GetTimeOffset());

    g->GetXaxis()->SetTimeDisplay(1);
    g->GetXaxis()->SetTimeFormat("%H:%M:%S");
    g->GetXaxis()->SetNdivisions(407);
    gPad->Modified();
    gPad->Update();
    gSystem->Sleep(delay);
  }
}

rw.C

// How to write a Tree in one process and view it from another process
// https://root.cern.ch/root/html/TTree.html#TTree:AutoSave

// https://root.cern.ch/phpBB3/viewtopic.php?f=3&t=19051
// root.cern.ch/files/fw.C

#include "TFile.h"
#include "TH1F.h"
#include "TPad.h"

void writer()
{
  TFile *f = new TFile("test.root", "RECREATE");
  TH1F *h = new TH1F("h", "h", 100, -3., 3.);
  f->Write(0, TObject::kWriteDelete); // ??? WHY ???
  Int_t count = 0;
  while(kTRUE) {
    printf("Loop %d\r", count++);
    fflush(stdout);
    h->FillRandom("gaus", 100);
    h->Write(0, TObject::kWriteDelete);
    f->SaveSelf();
    sleep(1);
  }
}

void reading(TFile *f, const char *name = "h")
{
  f->ReadKeys();
  delete f->FindObject(name);
  TH1F *h; f->GetObject(name, h);
  h->Draw();
  gPad->Update();
  gPad->Modified();
}

// []$ root
// root [0] .L rw.C+
// root [1] writer()

// []$ root
// root [0] .L rw.C+
// root [1] TFile *f = TFile::Open("test.root", "READ");
// root [2] while(kTRUE) { reading(f); gSystem->Sleep(1000); }