Changes between Version 4 and Version 5 of FAQ-General-4

Timestamp:

Feb 15, 2016, 10:40:11 AM (8 years ago)

Author:

Olivier Mattelaer

Comment:

--

FAQ-General-4

@@ +1 @@
+=== 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
+}}}
 
 
-=== 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
-