Next-to-leading order QCD cross-section Monte Carlo programs are used for comparisons of QCD perturbation theory and experimental data. Nowadays three programs are available, which allow user defined observables; these are MEPJET[1], DISENT[2], and DISASTER++[3]. With the availability of different programs cross-checks get important. To make a comparison the user code has to be implemented for each program. This procedure is susceptible to bugs and updating of several versions needs a decent revision control system.
To eliminate this additional source of error, a common scheme was developed and is presented here. The scheme consists of three independent parts, which are described in the following sections.
Section 2 introduces the steering card. This file is read at the beginning of each calculation and sets up the most important parameters. The user has the ability to add additional parameters to steer his own user routines.
The interface to the user routines is described in section 3. This code calculates the observables the user is interested in. For most standard procedures, e.g. performing boosts to different frames or calculating the number of jets, special functions are available in a library. These functions are explained in detail in section 5.