Can I just calculate the amplitudes for a (sub)process and check them point-by-point in phase space points using MadGraph ?

The easiest way to do this is to download the StandAlone MadGraph package and generate the process. You can then easily choose which diagrams to include in the matrix.f files of the SubProcesses/P_xx_xxxx directories. There is also an example program (check_sa.f) in the SubProcesses directory which shows how to calculate the amplitude at specific phase space points or by using PS configurations from RAMBO.

-- Main.FabioMaltoni - 02 Mar 2009