Program structure

Physics events are generated with the 2 steps; the MC integration step by the executable: integ and the event generation step by the executable: spring, as illustrated in Fig.3. In both steps, the program is controlled by an ASCII file: grape.cards. The file is read by the executables with help of FFREAD [#!FFREAD!#]. The contents of grape.cards are explained in the next section.

In the integration step by the executable: integ, an effective total cross-section (in unit of pb) and probability distributions are calculated by BASES [#!BS!#]. The results are stored in a file: bases.rz which has the Ntuple format provided by the HBOOK package [#!HBOOK!#]. At the same time, the information related to the convergency status of the integration is output into an ASCII file: bases.result.

In the event generation step by the executable: spring, unweighted events are generated. This is done by an routine: SPRING [#!BS!#] according to the probability distributions in bases.rz. The results of the event generation are stored in the PYTHIA common block /PYJETS/. After filling /PYJETS/, spring calls a routine: USRSTR in which user specific procedures are put. Its template is found in the appendix. The event information in /PYJETS/ is also available in a Ntuple file: grp.rz.

The calculated cross-section is found in bases.result or at the end of the standard output from spring. The status of the event generation is output into an ASCII file: spring.result. Looking at the file, users should find a reasonable agreement between generated distributions by spring and calculated ones by integ. The procedure to make the executables is described in the README file.

Fig. 3: Flowchart for the program structure