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% ROOT Version 6.22 Release Notes % 2020-05-19

Introduction

ROOT version 6.22/00 is scheduled for release in May, 2020.

For more information, see:

http://root.cern

The following people have contributed to this new version:

Guilherme Amadio, CERN/SFT,
Bertrand Bellenot, CERN/SFT,
Jakob Blomer, CERN/SFT,
Rene Brun, CERN/SFT,
Philippe Canal, FNAL,
Olivier Couet, CERN/SFT,
Andrei Gheata, CERN/SFT,
Enrico Guiraud, CERN/SFT,
Stephan Hageboeck, CERN/SFT,
Sergey Linev, GSI,
Pere Mato, CERN/SFT,
Lorenzo Moneta, CERN/SFT,
Alja Mrak-Tadel, UCSD/CMS,
Jan Musinsky, SAS Kosice,
Axel Naumann, CERN/SFT,
Vincenzo Eduardo Padulano, CERN/SFT and UPV,
Danilo Piparo, CERN/SFT,
Timur Pocheptsoff, Qt Company,
Renato Quagliani, LPNHE, CNRS/IN2P3, Sorbonne Université,
Fons Rademakers, CERN/SFT,
Oksana Shadura, Nebraska,
Enric Tejedor Saavedra, CERN/SFT,
Matevz Tadel, UCSD/CMS,
Vassil Vassilev, Princeton/CMS,
Wouter Verkerke, NIKHEF/Atlas,
Stefan Wunsch, CERN/SFT

Deprecation and Removal

  • ROOT::GetImplicitMTPoolSize has been deprecated in favor of the newly added ROOT::GetThreadPoolSize and will be removed in v6.24.
  • Manually setting TThreadedObject::fgMaxSlots is deprecated: TThreadedObject now increases the number of slots on-demand rather than running out and throwing an exception

Core Libraries

  • ROOT comes with C++ Modules enabled. More details about the technology found here.
  • The ACLiC can be configured to pass options to the rootcling invocation by enabling in the .rootrc the ACLiC.ExtraRootclingFlags [-opts] line.
  • A call to ROOT::EnableThreadSafety is not required before using TThreadExecutor or TTreeProcessorMT anymore
  • TTreeProcessorMT does not silently activate implicit multi-threading features anymore. An explicit call to ROOT::EnableImplicitMT is required instead
  • TTreeProcessorMT now has a constructor argument to set the number of threads for its thread-pool

I/O Libraries

TTree Libraries

  • A new status bit was added to TTree: kEntriesReshuffled, which indicates a TTree that is the output of the processing of another tree during which its entry order has been changed (this can happen, for instance, when processing a tree in a multi-thread application). To avoid silent entry number mismatches, trees with this bit set cannot add friend trees nor can be added as friends, unless the friend TTree has an appropriate TTreeIndex.

Histogram Libraries

Math Libraries

RooFit Libraries

RooWorkspace::Import() for Python

RooWorkspace.import() cannot be used in Python, since it is a reserved keyword. Users therefore had to resort to getattr(workspace, 'import')(...) Now, workspace.Import(...) has been defined for the new PyROOT, which makes calling the function easier.

Modernised category classes

RooFit's categories were modernised. Previously, the class RooCatType was used to store category states. It stores two members, an integer for the category index, and up to 256 characters for a category name. Now, such states are stored only using an integer, and category names can have arbitrary length. This will use 4 instead of 288 bytes per category entry in a dataset, and make computations that rely on category states faster.

The interface to define or manipulate category states was also updated. Since categories are mappings from state names to state index, this is now reflected in the interface. Among others, this is now possible:

ROOT 6.22 Before (still supported)
RooCategory cat("cat", "Lepton flavour"); RooCategory cat("cat", "Lepton flavour");
cat["electron"] = 1; cat.defineType("electron", 1);
cat["muon"] = 2; cat.defineType("muon", 2);

See also Category reference guide.

Type-safe proxies for RooFit objects

RooFit's proxy classes have been modernised. The class RooTemplateProxy allows for access to other RooFit objects similarly to a smart pointer. In older versions of RooFit, the objects held by e.g. RooRealProxy had to be accessed like this: RooAbsArg* absArg = realProxy.absArg(); RooAbsPdf* pdf = dynamic_cast<RooAbsPdf*>(absArg); assert(pdf); // This should work, but the proxy doesn't have a way to check pdf->fitTo(...); That is, a RooRealProxy stores a pointer to a RooAbsArg, and this pointer has to be cast. There was no type safety, i.e., any object deriving from RooAbsArg could be stored in that proxy, and the user had to take care of ensuring that types are correct. Now, if one uses RooTemplateProxy pdfProxy; instead of RooRealProxy realProxy; in RooFit classes, the above code can be simplified to pdfProxy->fitTo(...);

Check the doxygen reference guide for RooTemplateProxy for more information on how to modernise old code.

HistFactory

Switch default statistical MC errors to Poisson

When defining HistFactory samples with statistical errors from C++, e.g. Sample background1( "background1", "background1", InputFile ); background1.ActivateStatError(); statistical MC errors now have Poisson instead of Gaussian constraints. This better reflects the uncertainty of the MC simulations. This can be reverted as follows: // C++: Channel chan("channel1"); chan.SetStatErrorConfig( 0.05, "Gauss" ); // Within <Channel ... > XML:

Less verbose HistFactory

HistFactory was very verbose, writing to the terminal with lots of cout. Now, many HistFactory messages are going into RooFit's message stream number 2. The verbosity can therefore be adjusted using RooMsgService::instance().getStream(2).minLevel = RooFit::PROGRESS;

hist2workspace is also much less verbose. The verbosity can be restored with hist2workspace -v or -vv.

2D Graphics Libraries

  • Universal time (correct time zone and daylight saving time) in PDF file. Implemented by Jan Musinsky.
  • The crosshair type cursor type did not work on MacOS Catalina. This has been fixed by Timur Pocheptsoff.
  • Take into account the Z errors when defining the frame to paint a TGraph2DErrors.
  • Implement the of "F" in TPad::RedrawAxis to allow the plot's frame redrawing when erased.
  • Implement TCanvas::SetRealAspectRatio to resize a canvas so that the plot inside is shown in real aspect.
  • New graphics style "BELLE2" from Martin Ritter.

3D Graphics Libraries

Geometry Libraries

Geometry drawing in web browser

When ROOT compiled with -Droot7=ON flag, one can enable geometry drawing in web browser. Just apply --web option when starting root like: root --web tutorials/geom/rootgeom.C Not all features of TGeoPainter are supported - only plain drawing of selected TGeoVolume

Database Libraries

Networking Libraries

GUI Libraries

Montecarlo Libraries

PROOF Libraries

Language Bindings

JavaScript ROOT

Tutorials

Class Reference Guide

Build, Configuration and Testing Infrastructure

By default, ROOT now falls back to the built-in version of xrootd if it can't find it in the system. This means that passing -Dbuiltin_xrootd=ON is not necessary anymore to build ROOT with xrootd support. Note that built-in xrootd requires a working network connection.

Experimental address sanitizer build configuration

Added a build flag asan that switches on address sanitizer. It's experimental, so expect problems. For example, when building with gcc, manipulations in global variables in llvm will abort the build. Such checks can be disabled using environment variables. Check the address sanitizer documentation or the link below for details. In clang, which allows to blacklist functions, the build will continue.

See core/sanitizer for information.

Optimization of ROOT header files

Many (but intentionally not all) unused includes were removed from ROOT header files. For instance, #include "TObjString.h" and #include "ThreadLocalStorage.h" were removed from TClass.h. Or #include "TDatime.h" was removed from TDirectory.h header file . Or #include "TDatime.h" was removed from TFile.h. This change may cause errors during compilation of ROOT-based code. To fix it, provide missing the includes where they are really required. This improves compile times and reduces code inter-dependency; see https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/WhyIWYU.md for a good overview of the motivation.

Even more includes will be "hidden" when ROOT configured with -Ddev=ON build option. In that case ROOT uses #ifdef R__LESS_INCLUDES to replace unused includes by class forward declarations. Such dev builds can be used to verify that ROOT-based code really includes all necessary ROOT headers.

RDataFrame

  • Starting from this version, when RSnapshotOptions.fMode is "UPDATE" (i.e. the output file is opened in "UPDATE" mode), Snapshot will refuse to write out a TTree if one with the same name is already present in the output file. Users can set the new flag RSnapshotOption::fOverwriteIfExists to true to force the deletion of the TTree that is already present and the writing of a new TTree with the same name. See ROOT-10573 for more details.
  • RDataFrame changed its error handling strategy in case of unreadable input files. Instead of simply logging an error and skipping the file, it now throws an exception if any of the input files is unreadable (this could also happen in the middle of an event loop). See ROOT-10549 for more details.
  • New analysis examples based on the recent ATLAS Open Data release (Higgs to two photons, W boson analysis, Higgs to four leptons)
  • An exception is now thrown in case the size of ROOT's thread-pool changes between RDataFrame construction time and the time the event loop begins.
  • Just-in-time compilation of large portions of the computation graph has been optimized, and it is now much faster. Please report any regressions you might encounter on our issue tracker.
  • MakeRootDataFrame is now a safe way to construct RDFs. It used to return RDFs with more limited functionality.

PyROOT

  • Introduce the ROOT.Numba.Declare decorator which provides a simple way to call Python callables from C++. The Python callables are just-in-time compiled with numba, which ensures a runtime performance similar to a C++ implementation. The feature is targeted to improve the performance of Python based analyses, e.g., allows seamless integration into RDataFrame workflows. See the tutorial pyroot004_NumbaDeclare.py for further information.