Changes between Initial Version and Version 1 of FAQ-General-15

Timestamp:

Aug 20, 2016, 1:33:01 AM (8 years ago)

Author:

Olivier Mattelaer

Comment:

--

FAQ-General-15

@@ +1 @@
+=How can I remove some unwanted diagram?
+
+== Warning
+
+Be carefull about gauge invariance (a non gauge invariant subset will also break lorentz invariance)
+
+== Requirements:
+
+ 1. This method is implemented since MG5aMC version 2.5.0
+ 1. This method is only implemented for leading order processes
+
+== method:
+
+=== user_filter.py
+
+You need to define the file user_filter.py who should define the function remove_diag(diag):
+It should return True if you want to discard the diagram.
+
+example of file
+{{{
+def remove_diag(diag):
+    """remove all diagram with quark in T-channel"""
+    for vertex in diag['vertices']: #last
+         if vertex['id'] == 0: #special final vertex
+             continue
+         if vertex['legs'][-1]['number'] < 3: #this means T-channel
+             if abs(vertex['legs'][-1]['id']) <6:
+                  return True
+    return False
+}}}
+
+=== running with user_filter
+
+to activate the filtering, you have to add '--diagram_filter'
+to the command 
+example
+{{{
+generate p p > w+ w+ j j --diagram_filter
+}}}
+
+If you remove any diagram you should see on the screen:
+{{{
+INFO: Trying process: c c > w+ w+ s s WEIGHTED<=6 @1
+WARNING: Diagram filter is ON and removed 12 diagrams for this subprocess.
+}}}