Update History

• The manual contained on these html/php pages is kept up to date. (However, the "Brief Introduction" may not always be.)
• 8.1 is a quite new code, so there are many minor changes that, if all were to be documented, would hide the key ones.
• 8.1 is not yet used for "mission critical" applications, so there is less need to trace changed behaviour.

Main news by version

• 8.101: 10 November 2007
  • New option to initialize with arbitrary beam directions
    pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)
  • The LHAevnt and LHAinit classes have been joined into a new LHAup one, with new options that allow the writing of a Les Houches Event File.
• 8.102: 6 December 2007
  • Limited capability to use two different Pythia instances for signal + pileup event generation, see main19.cc for an example.
  • Added capability to set beam energy spread and beam vertex.
    Warning: as a consequence, some settings names have been changed, see below.
• 8.103: 22 January 2008
  • Updated HepMC conversion routine.
  • In the Event class the = and =+ methods have been overloaded to allow the copying or appending of event records. Illustrated in main19.cc.
• 8.104: 14 February 2008
  • Updated configure scripts.
  • The SusyLesHouches class updated to handle SLHA version 2.
  • The forceHadronLevel() method introduced for standalone hadronization.
  • main15.cc illustrated how either full hadronization or only decays of some particles can be looped over for the rest of the event retained.
  • The html and php page formatting improved with cascading style sheets.
  • The static ErrorMsg class has been removed and its functionality moved into the non-static Info class, in the renamed Info file.
• 8.105: 24 February 2008
  • Further reduction of the use of static, with related code changes. This should allow to have several almost independent Pythia instances. Some static classes still remain, however, notably for random number generation and particle properties.
  • Several minor improvements and new options.
• 8.106: 11 March 2008
  • Improved handling of the Higgs width, relevant for massive and thereby broad resonance shapes.
• 8.107: 17 March 2008
  • Correction in the event record, so that the beam particles in line 1 and 2 do not have any mother according to the motherList method. Previously the "system" entry in line 0 was counted as their mother, which gave rise to an unexpected extra vertex in the conversion to the HepMC format.
• 8.108: 1 May 2008
  • Support for HepMC version 1 is removed, to simplify the code and reflect the evolution of the field.
  • Status codes are stored in HepMC only as 1 for existing and 2 for decayed or fragmented particles (whereas previously the original PYTHIA codes were used for the latter).
  • Parton densities are stored in HepMC as xf(x,Q^2) rather than the f(x,Q^2) used in (some) previous versions.
  • The SusyLesHouches class has ben updated so that reading is fully compatible with the SLHA2 standard.
  • The matrix elements for neutralino pair production have now been completed and checked.
  • A new compilation option -Wshadow is introduced and code is rewritten at all places where this option gave warnings.
  • Minor library correction to allow compilation with gcc 4.3.0.
  • Ensure that alpha_strong does not blow up, by introducing a minimal scale somewhat above Lambda_3 (roughly where alpha_strong = 10).
  • New methods isValence1() and isValence2() in the Info class.

Changes among settings names

• A '*' is used as wildcard.
• Names within brackets denotes also new/changed functionality.