+USE,PYTHIA.
+USE,PYTHIA6.
+USE,PYTHIA6x.into the cradle to replace LUEEVT by PYTHIA6. Note that both PYTHIA6 and PYTHIA6x are needed (x=1 or 2). The first card selects the PYTHIA6 routines and common block names, rather than the PYTHIA5/JETSET ones, while the second selects the right sizes of the common-block variables, which differ between PYTHIA6.1xx (flag PYTHIA61), and PYTHIA6.2xx (flag PYTHIA62). When running CRESGVEXE, add the value 'pythia6xxx/lib' (VMS) or 'libpythia6xxx.a', (UNIX) (where 6xxx is the version You want to run) as the 7:th argument to link to the PYTHIA6 libraries. (Possibly the path needs to be included, as well.) Note that the version of this library currently changes quite often! With some versions, the value '"pythia6xxx pythiad"' will be needed instead, to get the DATA-statements correctly loaded.
The remarks in chapter 4.1.2 on the initialisation of PYTHIA5 also applies to PYTHIA6.
Note that SGV internally uses some JETSET routines (KLU and LUCOMP in the detector simulation, LUCLUS,LUFOWO, LUSPHE and LUTHRU in the analysis). Hence, JETSET needs to be linked with the program, even if PYTHIA6 is used as the event generator. This is correctly done by the standard CRESGVEXE. The only place where the PYTHIA and JETSET versions coexist in the same routine is in the PYTHIA6-version of ZEUGEN, where the contents of the (double-precision) PYJETS is copied to the (single-precision) LUJETS. The detector simulation is then working with LUJETS. In the generator initialisation (ZEORD), the PYTHIA6 common-blocks are copied to single-precision ones, the steering cards are read, and the single-precision blocks are copied back. This is unluckily necessary because the free-format input routines (FFREAD) do not handle double-precision. However, this does not imply any loss of precision: there are no default parameters in pythia6 which are given with more decimals than what can be accomodated in a single-precision word. To be consistent, the two arrays MSTU and PARU are copied from PYDAT1 to LUDAT1, as well. These are the only steering variables that the JETSET-routines mentioned above are using, and (at present) their content is identical between PYTHIA and LUJETS, only the word-length differs.