[Rivet] Using Genser AlpGen and Charybdis

[Andy Buckley]

Doug Gingrich wrote:
> Hi Andy,
> 
> I'm not sure I understand how things are meant to work with this version of AGILe, 
> but here is something that should get us started.  Charybdis has 2 interfaces, one 
> to Pythia and another to Herwig.  The choice of which interface to use is selected 
> by a compile time flag -DPYTHIA.  Thus I have always had to build 2 versions of 
> charybdis to work with rivetgun.

I'm only just now following up on these emails with Doug about Charybdis some
time ago. Sorry about the delay!

I'm not quite sure how Genser builds AlpGen and Charybdis, but there aren't
explicit libs for Herwig and Pythia. Hence this mail, copied to the Genser
developers, which I hope will elicit a bit of explicit instruction ;)


CHARYBDIS
=========

Genser Charybdis' lib directory just contains a libcharybdis.so. I see this in
the README file:

---
Note that if the library is compiled as PYTHIA - compatible (default in
GENSER), the fragmentation with HERWIG is still possible, one should just have
4 herwig-specific routines appended to the main program, see examples.
---

I've had a look at examples/mainherwig.F and I'm not sure exactly which
routines are being referred to. Can anyone clear this up? I'm also seeing a
segfaulting problem with the Pythia version, which should work fine: the gdb
output is not very helpful, unfortunately. Any suggestions as to what might be
going wrong here? Are common block size mismatches possible?

For reference as to how these are being used, here's the AGILe interface code:

http://projects.hepforge.org/agile/trac/browser/trunk/src/Charybdis/CharybdisFPythia.cc
http://projects.hepforge.org/agile/trac/browser/trunk/src/Charybdis/CharybdisFHerwig.cc


ALPGEN
======

AlpGen 2.1.3b/.../lib contains libalpgen.so and libalpsho.so. I'm guessing the
second of these is related to attaching a showering generator, but not sure
about the details: can someone confirm whether they'd expect the AGILe
F{Pythia,Herwig}AlpGen interfaces to be able to work by just loading
libalp{gen,sho}? Or how we can fix the interfaces if they're broken. Here's the
AGILe code:

http://projects.hepforge.org/agile/trac/browser/trunk/src/AlpGen/AlpGenFPythia.cc
http://projects.hepforge.org/agile/trac/browser/trunk/src/AlpGen/AlpGenFHerwig.cc


Here's hoping we can get this sorted in the next couple of days, so that the
next AGILe release will work properly with Genser's AlpGen and Charybdis builds...

Andy