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<title>Sample Main Programs</title>
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<h2>Sample Main Programs</h2>
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Descriptions of available classes, methods and settings are all
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very good and useful. Ultimately they are necessary for you to
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be able to fine-tune your runs to the task at hand. To get going,
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however, nothing helps like having explicit examples to study.
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This is what is provided in the <code>examples</code> subdirectory,
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along with instructions how they should be run:
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<li><code>main00.cc</code> : does not exist, but it has been defined
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in the <code>Makefile</code>, so this name could be used for a simple
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<li><code>main01.cc</code> : a simple study of the charged multiplicity
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for jet events at the LHC. (Brief example fitting on one slide.)</li>
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<li><code>main02.cc</code> : a simple study of the <i>pT</i> spectrum
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of Z bosons at the Tevatron. (Brief example fitting on one slide.)</li>
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<li><code>main03.cc</code> : a simple study of several different kinds
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of events, with the choice to be made in the <code>main03.cmnd</code>
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<li><code>main04.cc</code> : tests of cross sections, multiplicities and
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average transverse momenta for elastic, diffractive and nondiffractive
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topologies, using <code>main04.cmnd</code> to pick processes.</li>
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<li><code>main05.cc</code> : generation of QCD jet events at the LHC,
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with jet analysis using the <code>SlowJet</code> inclusive anti-<i>kT</i>
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sequential-recombination finder and the <code>CellJet</code>
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<li><code>main06.cc</code> : generation of LEP1 hadronic events, i.e.
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<i>e^+e^- -> gamma*/Z^0 -> q qbar</i>, with charged multiplicity,
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sphericity, thrust and jet analysis.</li>
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<li><code>main07.cc</code> : set up a fictitious production process
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to a generic resonance, where you easily can compose your own list
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of (two-body) decay modes to a variety of final states. Also traces
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decay chains down to truly stable particles: gamma, e+-, p/pbar and
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neutrinos. Suitable for astroparticle applications, like neutralino
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pair annihilation, where cross sections are calculated separately
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<li><code>main08.cc</code> : generation of the QCD jet cross section
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by splitting the run into subruns, each in its own <i>pT</i> bin,
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and adding the results properly reweighted. Two options, with limits
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set either in the main program or by subrun specification in the
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<code>main08.cmnd</code> file.</li>
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<li><code>main09.cc</code> : generation of two predetermined hard
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interactions in each event.</li>
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<li><code>main10.cc</code> : illustration how userHooks can be used
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interact directly with the event-generation process.</li>
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<li><code>main11.cc</code> : a study of top events, fed in from the
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Les Houches Event File <code>ttbar.lhe</code>, here generated by
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PYTHIA 6.4. This file currently only contains 100 events
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so as not to make the distributed PYTHIA package too big, and so serves
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mainly as a demonstration of the principles involved. </li>
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<li><code>main12.cc</code> : a more sophisticated variant of
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<code>main11.cc</code>, where two Les Houches Event Files
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(<code>ttbar.lhe</code> and <code>ttbar2.lhe</code>) successively
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are used as input. Also illustrating some other aspects, like the
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capability to mix in internally generated events.</li>
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<li><code>main13.cc</code> : a streamlined version of
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<code>main12.cc</code>, where two Les Houches Event Files
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(<code>ttbar.lhe</code> and <code>ttbar2.lhe</code>) successively
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are used as input in <code>main13.cmnd</code> file.</li>
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<li><code>main14.cc</code> : a systematic comparison of several
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cross section values with their corresponding values in PYTHIA 6.4,
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the latter available as a table in the code.</li>
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<li><code>main15.cc</code> : loop over several tries, either to redo
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B decays only or to redo the complete hadronization chain of an event.
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Since much of the generation process is only made once this is a way
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to increase efficiency.</li>
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<li><code>main16.cc</code> : put all user analysis code into a class
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of its own, separate from the main program; provide the "cards file"
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name as a command-line argument.</li>
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<li><code>main17.cc</code> : shows (a) how to use UserHooks to
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regularize onium cross section for pT -> 0, and (b) how decays
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could be handled externally.</li>
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<li><code>main18.cc</code> : shows how to write an event filter class,
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where you keep a vector of pointers to the subset of particles you
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want to study further. The event record itself remains unchanged.</li>
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<li><code>main19.cc</code> : use several instances of Pythia, one for
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signal events and others for a variable number of pileup and "beam-gas"
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events, combined into one common event record.</li>
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<li><code>main20.cc</code> : shows how PYTHIA 8 can write a Les Houches
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Event File, using facilities potentially useful also for other programs
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to write an LHEF.</li>
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<li><code>main21.cc</code> : an example how a single particle or various
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parton-level configurations can be input directly for hadronization,
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without being tied to the full process-generation machinery, e.g. to
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study the hadronization of junction topologies. </li>
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<li><code>main22.cc</code> : shows how an external resonance can be
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implemented as a new class derived from a PYTHIA base class, and be
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used in an external process, both of them handed in for generation
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as with normal internal classes.</li>
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<li><code>main23.cc</code> : shows how an external beam momentum spread
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and vertex location generator can be implemented as a new class derived
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from a PYTHIA base class, and then handed in for internal use.
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Also how to use an external random-number generator and an external
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parton distribution set.</li>
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<li><code>main24.cc</code> : tests of internally implemented cross sections
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for Supersymmetric particle production, with SYSY spectrum defined in
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<code>cmssm.spc</code> and settings in <code>main24.cmnd</code>. For
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illustration, an alternative example spectrum is also
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available, <code>sps1aWithDecays.spc</code>, which contains a decay
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table in SLHA format.</li>
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<li><code>main25.cc</code> : input RPV-SUSY events from an LHEF file that
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contains an SLHA spectrum inside its <code><header></code>. The
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event file, <code>main25.lhe</code>, contains a sample events that
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illustrate how to arrange color tags in the presence of the
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color-space epsilon tensors that accompany baryon number violating
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event topologies. </li>
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<li><code>main26.cc</code> : test program for processes in scenarios
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with large extra dimensions or unparticles. </li>
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<li><code>main27.cc</code> : production of Kaluza-Klein <i>gamma/Z</i>
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states in TeV-sized extra dimensions. </li>
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<li><code>main28.cc</code> : production of long-lived R-hadrons, that
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are forced to decay at a separate vertices and possibly with changed
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<li><code>main31.cc</code> : exemplifies an improved matching of
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parton showers to LHEF-style input based on the POWHEG approach.
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The <code>main31.cmnd</code> allows to switch between several
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different matching options. It also allows to select input process,
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in this case either for the POWHEG-hvq program applied to top
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pair production [<a href="Bibliography.php" target="page">Cor10</a>] or for QCD 2+3-jet events. The small
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samples of input events are stored in the <code>powheg-hvq.lhe</code>
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and <code>powheg-dijets.lhe</code> files, respectively.
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<li><code>main41.cc</code> : similar to <code>main01</code>, except that
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the event record is output in the HepMC event record format. Requires that
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HepMC is properly linked. Note that the <code>hepmcout41.dat</code> output
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file can become quite big; so no example is included in this
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<li><code>main42.cc</code> : a streamlined version for the generation
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of events that are then stored in HepMC format, without any event
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analysis. That is, all physics studies will have to be done afterwards.
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The name of the input "cards file" (e.g. <code>main42.cmnd</code>)
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and output HepMC event file (e.g. <code>hepmcout42.dat</code>) are to
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be provided as command-line arguments. Requires that HepMC is properly
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linked. Note that the HepMC output file can become quite big; so no
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example is included in this distribution.</li>
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<li><code>main51.cc</code> : a test of the shape of parton densities,
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as a check prior to using a given PDF set in a generator. Requires
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that LHAPDF is properly linked.</li>
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<li><code>main52.cc</code> : compares the charged multiplicity
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distribution, and a few other minimum-bias physics aspects, between
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default PYTHIA PDF and another one. Requires that LHAPDF is properly
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<li><code>main53.cc</code> : tests the possibility to do backwards
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evolution from an incoming photon at the hard interaction. Requires
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that you link to a LHAPDF set that includes the photon PDF.</li>
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<li><code>main61.cc</code> : a streamlined version for the generation
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of events that are then stored in HepMC format, without any event
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analysis. That is, just like <code>main42.cc</code>, with the difference
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that <code>main61.cc</code> can be used in conjunction with LHAPDF.
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The name of the input "cards file" (e.g. <code>main61.cmnd</code>)
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and output HepMC event file (e.g. <code>hepmcout61.dat</code>) are to
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be provided as command-line arguments. Requires that HepMC and LHAPDF
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are properly linked. Note that the HepMC output file can become quite
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big; so no example is included in this distribution.</li>
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<li><code>main62.cc</code> : a further extension of <code>main61.cc</code>,
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where subruns are used to process several consecutive LHEF,
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as in <code>main13.cc</code>, with information stored e.g in
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<code>main62.cmnd</code>. Other comments as for <code>main61.cc</code>.</li>
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<li><code>main71.cc</code> : an example how the FastJet jet finding
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package can be linked to allow an analysis of the final state,
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in this case for a study of W + jet production.</li>
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<li><code>main72.cc</code> : a comparison of SlowJet and FastJet
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jet finding, showing that they find the same jets if run under
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identical conditions, in this case for QCD jets.</li>
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<li><code>main81.cc</code> : do CKKW-L merging with a merging scale
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defined in <i>kT</i>. Input is provided by the <code>main81.cmnd</code>
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file and the three data files <code>w+_production_lhc_0.lhe</code>,
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<code>w+_production_lhc_1.lhe</code> and <code>w+_production_lhc_2.lhe</code>.
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<li><code>main82.cc</code> : do CKKW-L merging with a user-defined
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merging scale function. Input is provided by the <code>main82.cmnd</code>
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file and the three data files <code>w+_production_lhc_0.lhe</code>,
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<code>w+_production_lhc_1.lhe</code> and <code>w+_production_lhc_2.lhe</code>.
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<li><code>main83.cc</code> : as <code>main82.cc</code> but with an
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additional cut on the lowest multiplicity allowed for the reclustered
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state. The same input as for <code>main82.cc</code> can be used.
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<li><code>main84.cc</code> : do CKKW-L merging with output in such a way
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that it can be used in subsequent RIVET analyses. Input is provided by
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the <code>main84.cmnd</code> file and the three data files
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<code>w+_production_lhc_0.lhe</code>, <code>w+_production_lhc_1.lhe</code>
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and <code>w+_production_lhc_2.lhe</code>.
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<li><code>main91.cc</code> : exemplifies how you can link in runtime
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generation of hard processes from PYTHIA 6, using the Les Houches
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Accord facilities. This example is deprecated, since PYTHIA 8 by now
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contains essentially all hard processes found in PYTHIA 6.</li>
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In addition two main program illustrating the use of ROOT are available
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in the <code>rootexamples</code> subdirectory:
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<li><code>hist.cc</code> : shows how ROOT can be used for histogramming
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in a program that for the rest is structured like a normal PYTHIA run.
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<li><code>hist.cc</code> : shows how PYTHIA events can be stored as
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This subdirectory also contains a special Makefile and related
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