Go to the U of M home page
School of Physics & Astronomy
School of Physics and Astronomy Wiki

User Tools

Trace:
computing:contrib:root:localdoc

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
computing:contrib:root:localdoc [2009/02/19 09:30] – straitcomputing:contrib:root:localdoc [2009/06/01 15:47] (current) – more strait
Line 71: Line 71:
   void Loop(TTree * awesomedata)   void Loop(TTree * awesomedata)
   {   {
 +    yourdataobject * onedatum = 0;
 +    awesomedata->SetBranchAddress("yourdataobject", &onedatum);
     for(int i = 0; i < awesomedata->GetEntries(); i++){     for(int i = 0; i < awesomedata->GetEntries(); i++){
       awesomedata->GetEntry(i);       awesomedata->GetEntry(i);
Line 83: Line 85:
     Loop(awesomedata);     Loop(awesomedata);
   }   }
 +
 +The class "yourdataobject" needs only contain the data and not any functions.
  
 === Use Good Names === === Use Good Names ===
Line 100: Line 104:
  
 It outputs two short nouns stuck together.  It probably won't be very descriptive, but at least it will be searchable. It outputs two short nouns stuck together.  It probably won't be very descriptive, but at least it will be searchable.
 +
 +=== Avoid Unnecessary Pointers ===
 +
 +ROOT examples often declare //every// object as a pointer (with '*') and with dynamically allocated memory (with 'new').  For example:
 +
 +  TH1F * queengrid = new TH1F("it's a grid", "with queens", 10, 0, 10);
 +
 +This is dangerous because if you do not call:
 +
 +  delete queengrid;
 +
 +when you're done with the object, the memory is never released.  This is fine if you're just drawing one plot, but in a large program, you can quickly lose track of things like this and you will then wonder why it uses 3GB of RAM.  The alternative is:
 +
 +  TH1F queengrid("it's a grid", "with queens", 10, 0, 10);
 +
 +which, besides being safer, is also less typing.
 +
 +Now!  Graphical objects like histograms that are meant to appear on the screen //do// need to be allocated with 'new', because otherwise they will disappear from the screen when their function ends.  However, suppose you want to make a histogram, fill it and do a fit, but all you care about is the result of the fit; you never need to see the histogram.  Then declare the histogram without '*' and 'new'.
 +
 +For non-graphical objects like TRandom3, it's an easier call.  Don't make them pointers unless you have a particular reason to.  Despite the example you see that says to do this:
 +
 +  TRandom3 * laserfocus = new TRandom3();
 +
 +instead do simply:
 +
 +  TRandom3 laserfocus;
 +
 +These generate the same random numbers, but the first one stays in memory until you delete it explicitly, while the second stays in memory until the bottom of the function.  By the way, to pass each of these to another function, the functions are declared as:
 +
 +  // If you declared with '*' and 'new'
 +  void IWantRandomNumbers(TRandom3 * laserfocus)
 +  
 +  // If you simply declared the object:
 +  // This copies the object: the sequence of random
 +  // numbers will not be advanced in the calling function
 +  void IWantRandomNumbers(TRandom3 laserfocus)
 +  
 +  // This uses the object itself: the sequence of random
 +  // numbers *will* be advanced in the calling function
 +  void IWantRandomNumbers(TRandom3 & laserfocus)
  
 ===== How to Run Code ===== ===== How to Run Code =====
Line 105: Line 149:
 There are three generic options for running ROOT-based code: There are three generic options for running ROOT-based code:
  
-  # Interpreted in the ROOT (Cint) shell via running the program "root" +  - Interpreted in the ROOT (Cint) shell via running the program "root" 
-  # Compiled via running the program "root" +  - Compiled via running the program "root" 
-  # Compiled into a standalone executable+  - Compiled into a standalone executable
  
 The first two options are widely used and well documented (?) elsewhere.  Briefly, if one has the program "domyanalysis.C", it must contain the function domyanalysis().  It is run interpreted with The first two options are widely used and well documented (?) elsewhere.  Briefly, if one has the program "domyanalysis.C", it must contain the function domyanalysis().  It is run interpreted with
Line 137: Line 181:
  
    if(argc >= 2) seed = atoi(argv[1]);    if(argc >= 2) seed = atoi(argv[1]);
-   TRandom3 r(seed); +   TRandom3 atomlitre(seed); 
-   cout << "Your random number is " << r.Rndm() << endl;+   cout << "Your random number is " << atomlitre.Rndm() << endl;
        
    if(argc >= 3){    if(argc >= 3){
Line 157: Line 201:
 <code>printrandomnumber 17 datafile.root</code> <code>printrandomnumber 17 datafile.root</code>
  
-This has two big advantages.  First, you do not need to type all of those quotation marks and parentheses.  Second, your compiled program can run on machines that don't have ROOT installed.  Three advantages! Third, your code is less likely to stop working when the ROOT version changes.  Four, four advantages!  Fourth, it probably runs faster because it doesn't have all the overhead of running root itself.+This has two big advantages.  First, you do not need to type all of those quotation marks and parentheses.  Second, your compiled program can run on machines that don't have ROOT installed.  Third, your code is less likely to stop working when the ROOT version changes.  Fourth, it probably runs faster because it doesn't have all the overhead of running root itself.  Fifth, your code looks much more like the ordinary C++ that most programmers are familiar with. Sixth, the compile error messages from g++ are **much** more helpful than those from the ROOT compiler. Ok, more than two. 
 + 
 +====== Making Attractive Plots ====== 
 + 
 +The default ROOT plot is quite nice for screen display.  However, when you print it or use it in a talk, you will discover that the background is grey, which is ugly and wastes toner.  The lines used for histograms and axes are often too thin for easy reading when shown in a talk or paper.  Canvases have beveled edges and legends have drop shadows; whiz-bang, but not really suitable for many environments. 
 + 
 +These things can all be modified either by fiddling with the individual objects or by setting things in the active TStyle.  This code sets things up in a sensible way, although you probably want to pick and choose to suit your own tastes: 
 + 
 +<code> 
 +void SetOKStyle() 
 +{ 
 +  TStyle* OKStyle = new  TStyle("OKStyle", "OK Default Style"); 
 + 
 +  // Colors 
 + 
 +  //set the background color to white 
 +  OKStyle->SetFillColor(10); 
 +  OKStyle->SetFrameFillColor(10); 
 +  OKStyle->SetFrameFillStyle(0); 
 +  OKStyle->SetFillStyle(0); 
 +  OKStyle->SetCanvasColor(10); 
 +  OKStyle->SetPadColor(10); 
 +  OKStyle->SetTitleFillColor(0); 
 +  OKStyle->SetStatColor(10); 
 + 
 +  // Get rid of drop shadow on legends 
 +  // This doesn't seem to work.  Call SetBorderSize(1) directly on your TLegends 
 +  OKStyle->SetLegendBorderSize(1); 
 + 
 +  //don't put a colored frame around the plots 
 +  OKStyle->SetFrameBorderMode(0); 
 +  OKStyle->SetCanvasBorderMode(0); 
 +  OKStyle->SetPadBorderMode(0); 
 + 
 +  //use the primary color palette 
 +  OKStyle->SetPalette(1,0); 
 + 
 +  //set the default line color for a histogram to be black 
 +  OKStyle->SetHistLineColor(kBlack); 
 + 
 +  //set the default line color for a fit function to be red 
 +  OKStyle->SetFuncColor(kRed); 
 + 
 +  //make the axis labels black 
 +  OKStyle->SetLabelColor(kBlack,"xyz"); 
 + 
 +  //set the default title color to be black 
 +  OKStyle->SetTitleColor(kBlack); 
 + 
 +  //set the margins 
 +  OKStyle->SetPadBottomMargin(0.15); 
 +  OKStyle->SetPadLeftMargin(0.15); 
 +  OKStyle->SetPadTopMargin(0.075); 
 +  OKStyle->SetPadRightMargin(0.15); 
 + 
 +  //set axis label and title text sizes 
 +  OKStyle->SetLabelSize(0.05,"xyz"); 
 +  OKStyle->SetTitleSize(0.07,"xyz"); 
 +  OKStyle->SetTitleOffset(0.9,"xyz"); 
 +  OKStyle->SetStatFontSize(0.05); 
 +  OKStyle->SetTextSize(0.07); 
 +  OKStyle->SetTitleBorderSize(0); 
 + 
 +  //set line widths 
 +  OKStyle->SetHistLineWidth(2); 
 +  OKStyle->SetFrameLineWidth(2); 
 +  OKStyle->SetFuncWidth(2); 
 + 
 +  // Misc 
 + 
 +  //align the titles to be centered 
 +  //OKStyle->SetTextAlign(22); 
 + 
 +  //turn off xy grids 
 +  OKStyle->SetPadGridX(0); 
 +  OKStyle->SetPadGridY(0); 
 + 
 +  //set the tick mark style 
 +  OKStyle->SetPadTickX(1); 
 +  OKStyle->SetPadTickY(1); 
 + 
 +  //don't show the fit parameters in a box 
 +  OKStyle->SetOptFit(0000); 
 + 
 +  //set the default stats shown 
 +  OKStyle->SetOptStat("neimr"); 
 + 
 +  //marker settings 
 +  OKStyle->SetMarkerStyle(8); 
 +  OKStyle->SetMarkerSize(0.7); 
 + 
 +  // Fonts 
 +  OKStyle->SetStatFont(12); 
 +  OKStyle->SetLabelFont(12,"xyz"); 
 +  OKStyle->SetTitleFont(12,"xyz"); 
 +  OKStyle->SetTextFont(12); 
 + 
 +  // Set the paper size for output 
 +  OKStyle->SetPaperSize(TStyle::kUSLetter); 
 + 
 +  //done 
 +  OKStyle->cd(); 
 + 
 +  cout << "Using OKStyle" << endl; 
 +} 
 +</code> 
 + 
computing/contrib/root/localdoc.1235057411.txt.gz · Last modified: 2009/02/19 09:30 by strait

Page Tools