NEWS

Release Notes for fastjet
-------------------------

================================================================
Summary of changes from v2.4 -> v3.0beta1:  10 August 2011
================================================================

FastJet 3.0beta1 includes the majority of the features expected for
the 3.0 series and an interface that should now mostly remain
stable. The major new features relative to the 2.4.x series are:

- PseudoJets are aware of their structure, e.g. you can ask for jet.constituents()

- It is possible to associate arbitrary user information with a PseudoJet.

- Selectors, which allow easy communication of cuts across different functions

- Filtering, Trimming and a few boosted object taggers included
  natively as part of a new "Transformers" framework.

- New background estimation interface, with
  JetMedianBackgroundEstimator and GridMedianBackgroundEstimator
  classes.

- Improved doxygen and examples

- Many smaller changes, including aids for easier memory management,
  two new plugins, enhanced fortran wrappers and elimination of the
  R<pi /2 restriction on native jet algorithms 

See below for a more complete list of changes, including those
relative to the alpha releases.

In a few places, behaviour has changed from the 2.4.X series to
the 3.0 series:

- by default a JetDefinition is initialised to undefined_jet_algorithm
  instead of kt_algorithm with a radius of 1.

- JetDefinition::DefaultRecombiner sets the user index of the result
  of the recombination to -1 (the default for a PseudoJet; previously
  was being set to 0)

- ghosts are placed more sensibly in 3.0 than in the 2.X series;
  call ghost_area_spec.set_fj2_placement(true) to reinstate old behaviour

- CS::exclusive_subjets used to silently return fewer subjets than
  requested if there were too particles in a jet; to be consistent
  with exclusive_jets(...) it now throws an exception; use
  exclusive_jets_up_to(...) and exclusive_subjets_up_to(...) to avoid
  the exception.

- ATLASCone and TrackJet plugins use stable_sort instead of sort for
  more stable behaviour across architectures and compiler versions;
  this can change clustering results in events with degeneracies.

- some legacy headers have been removed (include/FjPseudoJet.hh and
  include/FjClusterSequence.hh), and some classes are deprecated:
  ClusterSequenceWithArea (use ClusterSequenceArea instead),
  ActiveAreaSpec (use GhostedAreaSpec instead), and RangeDefinition
  and CircularRange (use Selector instead)

- the plugins are by default built in a single 'libfastjetplugin'
  library. This is transparent if you use the fastjet-config script.
  The previous behaviour (each plugin in its own library) can be
  recovered by passing the --disable-monolithic option to configure.




================================================================
Summary of changes from v3.0alpha3 -> v3.0beta1:  10 August 2011
================================================================
New features
- Reorganised background estimation to have a JetMedianBackgroundEstimator
  and a GridMedianBackgroundEstimator (derived from BackgroundEstimatorBase)
  [v3.0alpha3 programs should replace BackgroundEstimator 
   -> JetMedianBackgroundEstimator, and use a new order of constructor arguments]
- Added the GridJetPlugin
- added a TopTaggerBase and a Johns Hopkins top tagger (JHTopTagger)
- to JetDefinition added delete_plugin_when_unused(), 
  delete_recombiner_when_unused()
- improved Filter (for area and recombiner support, also works with a subtractor)
- added a --config flag to fastjet-config

Bug fixes and other changes
- some speed gains in the default recombiner
- TrackJet and ATLASCone now use stable_sort (can change results;
  makes results stable across machine architectures & compilers, cf BUGS)
- fixed bugs in Voronoi areas (as in v.2.4.4) 
- fixed bugs in handling of empty areas in background estimator (as in 2.4.4)
- renamed SelectorMXXX -> SelectorMassXXX
- renamed NSubjettinessTagger -> RestFrameNSubjettinessTagger
- exclusive_[sub]jets(njets) now consistenty throws an error if it
  can't deliver njets; exclusive_[sub]jets_upto(njets) gives up to njets
- deprecated ClusterSequenceWithArea and ActiveAreaSpec
  (ClusterSequenceWithArea no longer available from
  ClusterSequenceArea.hh header)
- deprecated RangeDefinition & CircularRange; use Selector instead
- reorganisation of substantial parts of the manual


================================================================
Summary of changes from v3.0alpha2 -> v3.0alpha3:  03 June 2011
================================================================

New features
- Added a series of "Transformer"s in tools/:
   * Subtractor: subtract the jet using a BackgroundEstimator
   * Boost/Unboost: boosts/unboosts a jet
   * MassDropTagger: look for a mass drop in the jet substructure
   * NSubjettinessTagger: 2-pronged tagger based on rest-frame 2-subjettiness
   * CASubJetTagger: 2-pronged tagger based on maximal distance in jet history
   * Filter updated from alpha2 (bug fixes & new constructors)
  NB: examples 11 (boosted Higgs) and 12 (Filter) illustrate usage.

- CS::delete_self_when_unused() allows it to handle its own memory management
- GhostedAreaSpec can take a Selector to help specify ghost placement
- added a FunctionOfPseudoJet<T> base class to help standardise tool interfaces
- ClusterSequence::transfer_from_sequence now allows for a
  FunctionOfPseudoJet<PseudoJet> argument to transform (e.g. boost)
  the jets from an old sequence as they are transferred to the new one
- fortran interface now has basic area functionality

Changes to features introduced in alpha2 and alpha1:
- Numerous changes to BackgroundEstimator 
    * it allows manual encoding of rapidity dependence;
    * it can calculate density of quantities other than pt;
    * it has additional constructors, plus methods to reset its ClusterSequence, etc.
    * its sigma() now properly handles finite numbers of jets (+ other bug fixes).
- jet.pieces() for a jet from a clustering now returns the two parents
- various changes to behaviour of a jet's structural calls; see new table in doc
- PseudoJet::extra_properties<...>() -> PseudoJet::structure_of<...>() (cf example 12)
- join(...) can now include a recombiner argument; it also now supports areas
- Selector::count(jets) to know how many pass a cut (also new: Selector::sift)

Other changes 
- by default a PseudoJet is constructed with zero momentum
- by default a JetDefinition has an undefined_jet_algorithm
- efficiency improvements in PtYPhiM and ghost generation
- all uses of RangeDefinition now replaced by Selector. Old interfaces
  retained, but deprecated.
- added an example (09) to illustrate how to add user-info to a PseudoJet
- doxygen output now configured with an internal search engine

Bug fixes
- the default recombiner used to set the user_index to the non-default
  value of 0. Now it sets it to the default (-1).
- fixed crashes of VoronoiAreas for particles on a grid (also in 2.4.3)


================================================================
Summary of changes from v3.0alpha1 -> v3.0alpha2:  10 March 2011
================================================================

New features:
- two jets, a and b can now be joined:  PseudoJet c = join(a,b),
  intended to facilitate packaging the result of substructure tools;
  individual pieces can be recovered with c.pieces();
- New PseudoJetStructureBase class, to help implement such features
- New fastjet/tools/Filter.hh provides a unified interface to filtering and trimming
- New very preliminary fastjet/tools/BackgroundEstimator.hh to provide
  a more flexible interface to estimation of backgrounds (removal of
  hardest jets, etc.).
- a few extra Selectors

Changes to features introduced in alpha1:
- Selector is now in fastjet/Selector.hh (no longer fastjet/tools/...)
- Selector::relocate(...) and is_relocatable() renamed to
  Selector::set_reference(...) and takes_reference()
- PseudoJet::ExtraInfo has been renamed PseudoJet::UserInfoBase and
  corresponding access functions are now called set_user_info(...), etc.

Other changes and fixes
- some legacy headers removed
- bug fixes in NlnNCam strategies for R>pi

===========================================================
Summary of changes from v2.4.X -> v3.0alpha1:  27 January 2011
===========================================================

This is an alpha release, previewing some of the new features that are
expected to be available in FastJet version 3. Interfaces of new
features may yet evolve.

New features:
- Several extensions to PseudoJet:
  * it now knows what ClusterSequence it belongs to
  * info about internals of jets can be accessed e.g. as jet.constituents()
  * it now has a virtual destructor + other support for classes derived from PseudoJet
  * new facilities for associating user info with a jet (see PseudoJet::ExtraInfo)
  * some of these features make use of a new SharedPtr class 
    (intended mainly for advanced users)  
    similar to C++0x std::shared_ptr
  * calculation of phi and rapidity (cached) only on request
- R can now be taken larger than pi/2 for natively coded jet algorithms
- Addition of "Selector" tools through #include "fastjet/tools/Selector.hh"
- New plugin for D0RunICone (code contributed by Lars Sonnenschein)
- Improvements to fortran wrapper (access to SISCone, jet constituents, etc.)

Bug fixes:
- fixed issue with inconsistent returned sign in PseudoJet::delta_phi_to(...)

Other notable changes:
- Revamping of examples
- by default all plugins are now packaged into libfastjetplugins.
  Note that "external" libraries like libsiscone are still separate.
- Significant improvements to doxygen documentation

===========================================================
Summary of changes from v2.4.1 -> v2.4.2:  26 February 2010
===========================================================
- exclusive_ymerge_max(...) was not working; now fixed
- the D0RunIIConePlugin gave segfaults for some parameters; now fixed
- the D0RunIIConePlugin gave different results on 32/64 bit machines;
  optimisation flags now changed just for D0 code so that 32 bit gives same
  results as 64 bit. 
- changes to configure.ac to better handle fortran compiler checks
- removed some orphan/redundant code that was generating compilation warnings
- added an "--enable-monolithic" option to ./configure which causes
  all plugins to be placed in a single library (except SISCone)
- added a "--list-plugins" option to fastjet-config

=======================================================
Summary of changes from v2.4.0 -> v2.4.1:  29 May 2009
=======================================================

Fixes to the build system
-------------------------
- Included SISCone 2.0.1 (shared libs now enabled by default in
  SISCone too, and other small fixes)
- Fixed platform-dependent failures during make check
- Fixed gcc 4.4 compatibility issues (missing headers)
- Fixed a problem on Mac OS X with the arguments provided by
  "fastjet-config --libs" (--rpath versus -rpath).
- fastjet-config has new optional arguments (--rpath=no, --runpath)
  related to finding shared libraries at runtime on linux. 
  Run fastjet-config without any arguments for more info.
  To instead use static libraries, either configure with the
  --disable-shared option, or use fastjet-config with the --shared=no option.
- fastjet-config can now take --cxxflags and --libs in a single invocation
- With --cxxflags, fastjet-config now returns the minimal required set of arguments 
- Various other small mods (better fortran support, standardisation, ...)
  [thanks to Andy Buckley and David Grellscheid for suggestions]

Also
----
- Added a fortran wrapper for pp sequential recombination algorithms
- Fixed issue in median rho estimation when some jets have zero area
- Expanded descriptions that are returned by ATLAS/TrackJet/CMS plugins
- Warnings are no longer given when using exclusive jets with
  Cam/Aachen and certain e+e- algorithms (the warnings were misleading)
- Small fixes to the manual

=======================================================
Summary of changes from v2.3.X -> v2.4.0: 17 April 2009
=======================================================


New pp algorithms
-----------------

- added implementation of generalised kt algorithm (genkt_algorithm) for pp
- added D0RunIICone plugin [--enable-d0runiicone at configure time]
- added ATLASCone Plugin [--enable-atlascone at configure time]
- added CMSIterativeConePlugin [--enable-cmsiterativecone at configure time]
- added TrackJet Plugin (used by CDF in UE studies)
  [--enable-trackjet at configure time]

Introduction of e+e- algorithms
-------------------------------

- added an implementation of the e+e- kt algorithm (ee_kt_algorithm),
- added EECambridgePlugin for the (original) e+e- Cambridge algorithm
- added JADEPlugin for the JADE algorithm (see the ChangeLog or header
  file for details)
- added SISConeSphericalPlugin [enabled by default] for SISCone in
  e+e- and other spherical environments.
- native implementation of generalised kt algorithm for e+e- (ee_genkt_algorithm)
  [also provides access to e+e- form of anti-kt alg, conical jets on a sphere]
- added JadePlugin for the e+e- Jade algorithm

Meta-algorithms
----------------

- added NestedDefs plugin for daisy-chaining multiple jet definitions
  [still under testing; API may change in the future]

New functionality
-----------------
- added subjet functions for viewing jet at particular dcut, etc.
- added access to exclusive jets based on ycut as well as dcut (for e+e-)
- added support for asymmetric rapidity ranges in GhostedAreaSpec
- added support for a CircularRange (derived from RangeDefinition) for
  use in background estimation
- added class NNH to help users implement algorithms with
  user-chosen distance measure (see JadePlugin for an example)

Interface modifications
-----------------------
- removed default value of 0.5 for overlap_threshold in
  CDFMidPointPlugin, CDFJetCluPlugin and SISConePlugin constructors

  *** may break backwards compatibility ***

- a JetDefinition(jet_alg) constructor, without an R value, is no
  longer legal, except when jet_alg is ee_kt_algorithm (it has no R).

  *** may break backwards compatibility ***

- in SISCone, new way of accessing the information about pass at which
  a jet was found (old method retained for 2.4, but now deprecated)


Configure modifications
-----------------------
- added --enable-allplugins and --enable-allcxxplugins options, to
  avoid having to specify a long list of individual plugins
- shared libraries are now enabled by default

Bugs fixed
----------
- fixed missing support for periodicity in azimuth in RangeDefinition
  class

Other modifications
-----------------------
- added support for CGAL 3.4 (for non-standard locations, specify
  --with-cgaldir at configure time)
- removed restriction that fastjet throws exception on empty events
- added an example that illustrates the use of subjet techniques for
  a boosted Higgs->b+bbar search

Still to come
-------------
- add CMSIterativeCone Plugin



=======================================================================
Summary of changes from v2.3.3 -> v2.3.4 (bug fix release): 15 Aug 2008
==========================================================

- fixed infinite-loop bug in JetClu plugin on certain rare events

- fixed compatibility issues of certain example programs with g++-4.3

- incorporated SISCone 1.3.3 with similar g++-4.3 fixes

=======================================================================
Summary of changes from v2.3.2 -> v2.3.3 (bug fix release): 28 Apr 2008
==========================================================

- fixed missing installation of .../config_auto.h

- fixed missing typename in .../SearchTree.hh

=======================================================================
Summary of changes from v2.3.1 -> v2.3.2 (bug fix release): 03 Apr 2008
==========================================================

- fixes to propagation of CXXFLAGS through the build chain

- small change in Voronoi area code to fix crashes on regular
  (calorimeter) layouts of momenta

- small change in active areas code to fix crashes on algorithms that
  do not cluster all particles

- eliminated "using namespace std" that had accidentally been left in
  certain area header files

- incorporation of SISCone 1.3.2 with fixes for inappropriate public
  symbols and to build framework


======================================================================
Summary of changes from v2.3.0 -> v2.3.1 (bug fix release)
==========================================================

- Fixed compilation issues under windows VC7.1 (reported by
  I. Belyaev); also included SISCone 1.3.1 with similar fixes.

- Fixed speed issue under optimized compilation of CDF MidPoint plugin
  for 32 bit architectures that had arisen subsequent to the switch to
  autotools with its common optimization settings.

- Fixed "make check" failure with the --disable-siscone option.

- Fixed crash in exclusive_dmerge(njets) for njets=0 (reported by P. Lenzi)


======================================================================
Summary of changes from v2.1.0 (previous stable release) to v2.3.0
===================================

- added the anti-kt algorithm (LPTHE-07-03), which is a sequential
  recombination algorithm that gives conical jets.

- Added Passive and Voronoi areas, and new common class for accessing
  all types of areas, ClusterSequenceArea.

- switched to autotools for compilation and installation:
     ./configure --prefix=... 
     make
     make check      [optional]
     make install

  NB: users should no longer include fastjet-2.x.y/Makefile
  when building their own programs, and instead should use
    g++ -c file.cc `fastjet-config --cxxflags`
    g++ file.o `fastjet-config --libs --plugins` 

- plugin include files are now to be accessed with fastjet/ in 
  front of them, i.e.
    #include "fastjet/SISConePlugin.hh"
  A simple #include "SISConePlugin.hh" is now obsolete but will
  continue to work through 2.x

- Added RangeDefinition class to provide more flexibility in UE/pileup
  estimation.

- New facilities for navigating the cluster sequence (has_parents,
  has_child and has_partner members of ClusterSequence)

- other bug fixes and small enhancements (including SISCone-1.3.0,
  improvements to plugin facilities).

See individual beta-releases below for more information, as well as
the ChangeLog.


======================================================================
Changes from v2.2beta0 to v2.3-beta0
===================================

- switched to autotools for compilation and installation;

- old build procedure still available for now, with files called
  makefile.static  (make -f makefile.static); 

  test-script.sh has been renamed test-static.sh and builds and 
  tests using the old procedure.

- plugins include files are now to be accessed with fastjet/ in 
  front of them, i.e.
  #include "fastjet/SISConePlugin.hh"

  For backwards compatibility, the old access method will continue
  to work throughout v2.x, i.e.
  #include "SISConePlugin.hh"

- added PseudoJet::reset(...) functions to reset the contents of a
  PseudoJet.

- added fastjet_version_string()

- added a function PtYPhiM(...) that returns a PseudoJet with the
  given py, rapidity , phi and mass.  Defined in PseudoJet.hh

- added a directory fortran_wrapper/ to illustrate how to access
  fastjet from fortran

- some small bug fixes in the CDF midpoint code


======================================================================
Changes from v2.1.0 to v2.2beta0
===============================

- added the anti-kt algorithm (LPTHE-07-03)

- Provided  a new common class for accessing all different types of  
  areas: ClusterSequenceArea.

- added functionality for Passive areas and Voronoi areas. 
  Areas are now defined much in the same way as jets, via an 
  AreaDefinition, which is passed as an argument
  to ClusterSequenceArea. NB: the Voronoi area uses Fortune's
  sweepline code for calculating the Voronoi diagram and so does not
  require CGAL to be installed (it still is needed for NlnN kt
  clustering). 

- Added class RangeDefinition which allows detailed definitions
  of the rapidity-azimuth ranges over which to study jet areas
  and possibly perform noise subtraction

- added facilities for navigating the cluster sequence (has_parents,
  has_child and has_partner members of ClusterSequence)

- changed plugin base class, so that it now includes R() virtual
  member, and modified the various plugins to account for this.

- modified the plugin interface to provide facilities to help with
  passive areas.

- included SISCone-1.2.0 rather than 1.1.1.

- adapted SISCone plugin to the 1.2.0 release of SISCone -- main
  changes are facilities and improvements related areas: some speed
  improvements on the split-merge (relevant for active areas) and a
  fairly efficient way of running passive areas.

- added ClusterSequence::print_jets_for_root(...) and a corresponding root
  script (example/root/jet-plots.C), so as to provide a crude
  visualisation tool.


======================================================================
Summary of main changes from v2.0.0 to v2.1.0
=============================================

- added plugin structure for external jet finders.

- included plugins for SISCone, CDFMidPoint, CDFJetClu, PxCone (with
  extensions for MidPoint and bug fixes for PxCone relative to public
  codes).

- introduced option of control over recombination scheme, with a
  RecombinationScheme enum, which applies also to area_4vector.

- added description() member function to JetDefinition class, so 
  that you can get a (string) summary of what you're running!

- changed the default number of repeats in ActiveAreaSpec to 1 (which
  is sufficient for most purposes).

For further details, see the changes listed in detail below.

======================================================================
Changes from v2.1.0b4 to v2.1.0
===============================

- corrected bug in test-script.sh

- removed PxCone from default tests and from 
  plugins/usage_examples/many_algs_example.cc (to avoid fortran
  compilation issues).

======================================================================
Changes from v2.1.0b3 to v2.1.0b4
=================================

FastJet modifications
---------------------

- default number of repeats for the active area specification has been
  changed from 5 to 1 (the latter goes fast, but note that it provides
  a zero error estimate for the area).

Plugin modifications
--------------------

- adapted plugin to accomodate new scale for use in the SISCone
  split-merge (pttilde), with a corresponding change of interface.

  Changed default number of passes for SISCone to 0.
  
- Added the pttilde scale choice to the CDF plugin.



======================================================================
Changes from v2.1.0b2 to v2.1.0b3
=================================

FastJet enhancements
--------------------

- methods for estimating the underlying now have the option of using
  area_4vector rather than the plain area

FastJet bug fixes
-----------------

- area_4vector is now calculated with the same recombination scheme as
  the jets themselves

- massless recombination schemes now work correctly on particles with
  zero momentum

- PseudoJet::phi_std() returned wrong result for phi < pi -- thanks to
  Oscar Stal for pointing this out.

Plugin modifications
--------------------

- the plugin mechanism now allows a plugin to add "extra" information
  to the ClusterSequence, essentially by providing an auto_ptr to a
  class derived from (the new) ClusterSequence::Extras; an example of
  this has been implemented with siscone (SISConeExtras) which allows
  a user to access the initial (stable) protocones.

- included new siscone version (1.1) which uses transverse mass (mt) rather
  than pt in the split-merge procedure, to address an IR problem in
  events where the hadronic part conserves momentum -- this can have
  an effect on some physical distributions; the siscone update also
  addresses issues with collinear safety and co-circular points.

- included bug fixes to pxcone regarding 2pi periodicity when
  recombining momenta

- modified the version of the CDF midpoint cone code so as to allow it
  to use mt and Et as the parameters in the split--merge step.

======================================================================
Changes from v2.1.0b1 to v2.1.0b2
=================================

Bug fixes
---------

- included new siscone version which solves the memory-leak problem

Other changes
-------------

- added sample output from the test-script as test-script-output-orig.txt

======================================================================
Changes from v2.1.0b0 to v2.1.0b1
=========================

New features:
-------------

- added the SISCone plugin and the beta version of the siscone code
  (authored by Soyez & Salam)

Bug fixes
---------

- removed extraneous semicolons after functions that were causing
  problems on some compilers.

Other additions
---------------

- Added COPYING file with GPL license

======================================================================
Changes from v2.0 to v2.1 (beta0)
=========================

New features:
-------------

- introduced option of control over recombination scheme, with a
  RecombinationScheme enum (a variable of this type should be provided
  to the JetDefinition constructor) and also the possibility of an
  externally defined recombination scheme.

- introduced a "plugin" facility for alternative jet finders, via an
  abstract base class
 
    class JetDefinition::Plugin

  Plugins are to be provided as classes derived from this,
  implementing the relevant virtual functions (see manual and examples
  for further info).

- introduced "description" member function for the JetDefinition
  class, which returns a (std::string) textual description of the
  algorithm defined.

- provided plugins for CDF JetClu, CDF Midpoint, PxCone code; the
  plugins, the code they interface to and example programs are to be
  found in the new plugins/ directory.

- added ClusterSequence::unclustered_particles() a vector containing
  the unclustered particles (relevant for some plugin algorithms).

Minor additions
---------------

- introduced PseudoJet::squared_distance (does same as "plain_distance")



Notational changes:
-------------------

- in the documentation, replaced eta -> y, to make it clear that it's
  rapidity and not pseudorapidity that is being used throughout. Some
  internal code continues to use variables called "eta" -- but these
  are actually proper rapidity.


======================================================================
Changes from v1.0 to v2.0
=========================

New features:
-------------

- the longitudinally invariant inclusive Cambridge/Aachen jet finder
  has been added.

  Note that the exclusive jets extraction for the Cambridge jet-finder
  does not provide the definition as given in the original Cambridge
  paper. See the documentation for further details

- classes have been introduced for running jet clustering and
  simultaneously collecting information about the area of each jet. 
  The base class specifying the functionality is
   
    class ClusterSequenceWithArea;

  itself derived from ClusterSequence.

  Two derived classes that provide the actual areas functionality are:

    class ClusterSequenceActiveArea;
    class ClusterSequenceActiveAreaExplicitGhosts;

  To construct them, one also needs to specify how one wishes the area
  to be calculated, via a class

    class ActiveAreaSpec;


New optimizations:
------------------
- new clustering strategies have been added:
  
  
    N2MinHeapTiled : like N2Tiled, except that the non-geometric
                     part has been replaced with a N ln N algorithm
                     (overall the strategy still scales as N^2, but with a
                     smaller coefficient)

    NlnNCam, NlnNCam2pi2R, NlnNCam4pi:

                     NlnN strategies specific to the Cambridge/Aachen
                     jet-finder -- the fastest of them is NlnNCam.
                     Depending on the size of the event and of the CPU
                     cache it may be up to 2.5 times faster than the
                     CGAL-based NlnN strategy. Experiment on your own
                     hardware and events to establish whether the
                     speed gain is significant.

                     These strategies are based on the work on dynamic
                     Closest Pair problems by Timothy Chan.

    Best           : (was present before) now attempts to select best 
                     among N2Plain, N2Tiled, N2MinHeapTiled, NlnN. 

                     As the best option for a given N may depend on R
                     and the event structure, you are advised to
                     experiment with individual strategies if the
                     last few tens of percent in speed are critical.
                     


Updates to user interface
-------------------------

While the v1 interface to fastjet has been maintained for backwards
compatibility, for new developments in v2 and related forthcoming
work, a new interface is provided as follows:

- User accessible classes and enums have had the "Fj" prefix removed
  and are instead now in namespace fastjet; the corresponding include
  files are in the include/fastjet directory. So, for example instead
  of

    #include "FjClusterSequence.hh"
    //...
    FjClusterSequence clust_seq(...)

  one now uses the following

    #include "fastjet/ClusterSequence.hh"
    //...
    fastjet::ClusterSequence clust_seq(...)

  If typing "fastjet::" the whole time seems too long-winded, you can
  abbreviate "fastjet" as "fj" with

    namespace fj = fastjet;

  or eliminate the need for it altogether with

    using namespace fastjet;
  
- a new class, fastjet::JetDefinition, has been introduced for holding
  the details of the jet finder (which one, value of R, etc...) that
  is to be used in a given clustering.

    #include "fastjet/JetDefinition.hh"
    #include "fastjet/ClusterSequence.hh"
    //...

    double R = 0.7;

    // define jet algorithm
    fastjet::JetDefinition jet_def(fastjet::kt_algorithm, R);

    // get the cluster sequence for a vector of 4-momenta and the 
    // given jet definition
    fastjet::ClusterSequence clust_seq(momenta, jet_def);

- some errors that previously were assertions now throw an
  fastjet::Error -- exception. A fully uniform handling of exceptions
  is currently some way away however and users for whom this is an
  important issue should contact the authors.