=== 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 create a Standalone package: {{{ generate p p > e+ e- output standalone PATH }}} 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. You can also returns a valid c++ standalon code by running {{{ generate p p > e+ e- output standalone_cpp PATH }}} If you want to have acces to the matrix-element via python. The easiest is to have the fortran code wrapped into python (evaluating a matrix element in python is just too slow to be usable). Each of the SubProcesses/P_xx_xxxx of the standalone directory can be compiled to be python linkable (note this require f2py part of numpy and to have python-devel package installed): {{{ make matrix2py.so }}} Then you can link this from your python code. Here is an example: {{{ import matrix2py def invert_momenta(p): """ fortran/C-python do not order table in the same order""" new_p = [] for i in range(len(p[0])): new_p.append([0]*len(p)) for i, onep in enumerate(p): for j, x in enumerate(onep): new_p[j][i] = x return new_p matrix2py.initialise('../../Cards/param_card.dat') p = [[ 0.5000000E+03, 0.0000000E+00, 0.0000000E+00, 0.5000000E+03], [ 0.5000000E+03, 0.0000000E+00, 0.0000000E+00, -0.5000000E+03], [ 0.5000000E+03, 0.1109243E+03, 0.4448308E+03, -0.1995529E+03], [ 0.5000000E+03, -0.1109243E+03, -0.4448308E+03, 0.1995529E+03]] P =invert_momenta(p) alphas = 0.13 nhel = 0 # means sum over all helicity me2 = matrix2py.get_me(P, alphas, nhel) print me2 }}}