This is the README file for the EvtGen package

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Please send questions to:
David Lange lange@slac.stanford.edu
Anders Ryd ryd@hep.caltech.edu

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This is release alpha-00-09-42
It is known to compile/link on Linux/gcc321. Other unix
platforms should be straight forward, in the past we have 
run his code on SunOS, OSF, AIX and HP-UX also, but it is not tested for
this release.  

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The package is documented on the WWW page:

http://www.slac.stanford.edu/~lange/EvtGen/

The documentation is maintained in the directory doc in this
package. Please see doc/README for further information.

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To get started with EvtGen:

  - Have a look at the pitfalls section below.

  - Set a few envvars to tell EvtGen where you have
    installed CERNLIB, ROOT, and CLHEP. For me these  
    variables are 
  
1.    CERN_ROOT = /cern/pro
2.    ROOT_SYS = /home/lange/root
3.    CLHEP_BASE_DIR = /home/lange
         (CLHEP in /home/lange/CLHEP and
          CLHEP libs in /home/lange/lib)

  - Run the "configure" script in this directory.  

  - "make" will compile the EvtGen source code and create
    libEvtGen.a

  - "make bin" will build the executable testEvtGen which
    can be run from the "test" subdirectory with the command
    "../testEvtGen test1 1000" this executable has a C++ driver.

  - Additional information can be found in the documentation.

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Pitfalls

Depending on the details of your setup, there are various problems
that you might have while setting up EvtGen.  These primarily are
due to the interfaces with the PYTHIA and PHOTOS packages.  Below we
list the ones we know about.  We are trying to handle some of these in
the configure script, but have not done so in this version of the code.

The default code are tested against cernlib2002 and CLHEP 1.8.0.

Things you might need to change:

1. The names of the pythia and pdflib libraries are different in
different cernlib versions.  The error will be that "make bin"
will fail with "/usr/bin/ld: cannot find -lpythia6205", for
example. These may need to be changed in the Makefile.  For example, 
for cernlib 2001, pythia6205 will need to be changed to pythia6152


2. The pydat3 common block size may not be correct. If so, you will
get a warning during when building the binary. For example, for
if you are using cernlib 2001, you will see:

/usr/bin/ld: Warning: size of symbol `pydat3_' changed from 294000 to 150000 in pydata.o

to remove this warning, edit EvtGenModels/Pythia.F in two places.

      COMMON/PYDAT3/MDCY(500,3),MDME(8000,2),BRAT(8000),KFDP(8000,5)

should instead be

      COMMON/PYDAT3/MDCY(500,3),MDME(4000,2),BRAT(4000),KFDP(4000,5)


3. Using versions of cernlib before 2002, we get the error
     
 EvtGen:Pythia can not decay:Xu-
testEvtGen: EvtPythia.cc:210: virtual void EvtPythia::decay(EvtParticle*): Assertion `0' failed.

which is due to the Xu- particle being unknown to pythia.
(despite the Xu0 and Xu+ being defined).  We believe this can
be fixed by adding code to pycomp.F, but recommend commending out
the lines involving Xu- in DECAY.DEC if you can not use cernlib2002