Mig3to4

Rivet 4 is a major new release series, in which we’ve made some big changes that affect the programming interface (or “API”) exposed to analysis authors.

As with the last time we made such major changes, from version 2 to version 3, the overall effect is very positive, but code will need to be changed. We have made the changes to all the analyses submitted to the Rivet core library, so there’s another incentive to submit your analyses, too!

The 3 -> 4 changes particularly affect histogramming – which now requires the fully reworked YODA v2 – and the configuration of some projections. Version 4 also adds functionality for storing and loading analysis-specific structure data in HDF5 format, and other new features, but as those are not changes to existing functionality they aren’t covered in this migration guide.

• Behind the scenes a lot has changed in the histograms. However, the user interface for fillable histograms is still the familiar set of Counter, Histo1D/2D, Profile1D/2D, etc. If you wish, you can now also create higher-dimensional histograms or histograms with discrete axes.

• Reference data was previously stored as point+errorbar Scatter types, which did not have proper binnings. They are now stored as BinnedEstimate types when the reference data is actually binned. The API and user-facing behaviour should be very similar. Note that HepData already supports export options for both the new YODA format and the YODA1 legacy format.

• The (badly named) BinnedHistogram type that was basically a collection of histograms, themselves binned in an additional variable, has been replaced with the HistoGroup. This has the same aim and basic design, but is now literally implemented as a binning containing a Histo1D in each bin. It can be accessed via the predefined specialisations, Histo1DGroupPtr and Histo2DGroupPtr.

• Any “live” types of analysis objects left at the end of the finalize() stage will be automatically converted to “inert” estimate types, usually a BinnedEstimate1D, for direct equivalent to reference data. The /RAW pre-finalize copies will still be live types, allowing re-entrant finalization via rivet-merge. If you need to perform a custom conversion, e.g. to make the histogram inert without scaling by bin-width, you need to do that in finalize(), e.g. via the barchart() function.

• Many enums have been renamed, and unclear bool options (e.g. as arguments to projection constructors) have been converted to more self-documenting enums. Scoped enum classes are now used as standard, and are defined outside projection scopes, so there is now always exactly one set of :: per enum value (with the implicit Rivet:: namespace). This eliminates code smells like the mix of two- and three-layer enums, from both the JetAlg and FastJets scopes when configuring jet finders. Some renaming examples:

  • FastJets::Algo::KT -> JetAlg::KT,
  • JetAlg::Invisibles::NOPROMPT -> JetInvisibles::NONPROMPT,
  • JetAlg::Muons::NONE -> JetMuons::NONE
  • etc.

• Tau/mu as-prompt reco bools -> AsPromptTau/Mu enums. In general, all projection-config bools are now enum classes for better code-readability / self-documentation.

• DressedLeptons projection -> LeptonFinder. DressedLeptons is now a vector<DressedLepton> alias by analogy with Particles, Jets, etc.. The promptness bool-argument to the constructor is now a PromptOnly::YES/NO enum class.

  • Note that one of the constructors used to take a FinalState for photons followed by a FinalState for the bare leptons: This has now been swapped.

• WFinder has been removed: there are too many analysis options with the imperfect information induced by the invisible neutrino, so you should do it by hand. See the Doxygen API reference and existing analyses for guidance on e.g. using dressed leptons and MET via the LeptonFinder, and the new closestMatchIndex() metafunction used with the mass() and mT() functions.

• ZFinder has been canonically renamed to DileptonFinder and its trackPhotons option argument has been removed: if you do not want to include the photons, set the dressing dR radius to a negative number, conventionally -1. The constructor arguments have been changed, so the target mass now must be specified, and the mass-window and other cuts on the resulting dilepton vector are given via a single Cut argument. Again, see the Doxygen API reference and existing analyses for illustration.

• Jet smearing via SmearedJets now accepts multiple ordered smearing and efficiency functions via a parameter pack. This has required a re-ordering of parameters in a slightly non-optimal fashion, but was considered an overall preferable solution, especially given that this feature is a niche requirement!

• Several built-in analyses have been renamed, especially analyses for computing heavy-ion centrality curves, and MC_* decay analyses. These now match the ALL_CAPS convention used for other analyses, and a new conventional ordering of a CENT name-element for centrality plugins. The few analysis base classes, e.g. for all MC_*JETS and MC_*SPLITTINGS analyses, have also been renamed into a consistent scheme.

• Any old analyses previously named with an Sxxxxxx publication identifier corresponding to the legacy SPIRES database has now been renamed to match the newer analyses with Ixxxxxx Inspire-based codes. Previous aliasing to allow loading via the Inspire name has now been switched so the non-canonical alias is the SPIRES name. These fallback aliases will eventually be removed.

We recommend that anyone writing a new analysis should start by running the rivet-mkanalysis script rather than directly copying an old analysis code: we update the templates generated by the script as new API features and ideas occur, and it always represents best-practice. You can still copy-paste chunks from your old analysis as you need them, modulo the unavoidable API changes above.