[Rivet] HepMC 2.04.00 beta release

[Alberto Ribon]

  Dear colleagues,

  the HepMC 2.04.00 beta release is available:

    /afs/cern.ch/sw/lcg/external/HepMC/2.04.00.beta

  Notice that for this beta release only the library for 
  the platform  slc4_amd64_gcc34  is available.

  Some remarks:

    1)  x*f(x)  should be stored in PdfInfo.

	Two new integer data members have been added
        to the PdfInfo class, one for each beam, to 
        store the unique pdf-set id.    

    2)  The deprecated class  IO_ExtendedAscii  
        has been removed. 
        The deprecated class  IO_Ascii  is kept but 
        it is strongly discouraged, and will be
        removed next year, in HepMC 2.05.00 release.
        Users should use the class  IO_GenEvent .

    3)  Units, for momentum and positions, have been
        introduced. The choices are:
          -  momentum : UNKNOWN (default), MEV, GEV
          -  position : UNKNOWN (default), MM, CM
        Notice that "UNKNOWN" is assumed when the units
        are not specified, in order to guarantee backward
        compatibility with older files written with 
        previous versions of HepMC (which do not have units).
        Of course, although users are not forced to specify
        the units, specifying them is the officially supported
        way: it ensures forward compatibility!

    4)  Particle's status code : the HEPEVT convention 
        should be followed. 
        In practice, there is some difference in the range
        of status code values produced by the various MC 
        Event Generators. 
        We defer to next year, when the HepMC 2.05.00 release
        will be discussed in a dedicated LCG Generator Service
        monthly meeting, the important discussion, between
        MC authors and LHC experimentalists, about which 
        status code values should be available.


  For more details, see:

        http://lcgapp.cern.ch/project/simu/HepMC/20400/


  Please send your feedbacks to me and Lynn Garren
  possibly before  *** Friday 23 May *** .


  Best regards,
               Alberto