Changes between Version 3 and Version 4 of FAQ-General-15

Timestamp:

Jun 20, 2020, 8:45:58 PM (5 years ago)

Author:

Olivier Mattelaer

Comment:

FAQ-General-15

@@ -1 @@
-=How can I remove some unwanted diagram?
+== 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
+Additionally, this method is only implemented for leading order processes
 
 == method:
+ 1. You need to add a file PLUGIN/user_filter.py this file should define a function named "remove_diag" (see example below). The function should return True if you want to discard the diagram and False if you want to keep it.
+ 1. When running the code, you have to add the flag "--diagram_filter" 
+{{{
+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.
+}}}
 
-=== user_filter.py
+== example of user_filter.py for version of the code for  2.7.3 and later (and 3.0.2 and later)
 
-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 using the drawing module
+{{{
+import madgraph.core.drawing as drawing
 
-example of file
+def remove_diag(diag, model):
+    """remove all diagram with quark in T-channel"""
+
+    #diag is a Direct Accyclic Graph of the Feynman diagram
+    #convert it to a full graph (the one we used for the plotting)
+    #In that representation each vertex is associated to all the legs/particle and we can move quite freely inside the diagram
+    # The structure representation is simpler and should help to apply complex filtering
+
+    draw = drawing.FeynmanDiagram(diag, model)
+    draw.load_diagram()
+    print(draw._debug_load_diagram())
+    
+    # Diagram content  can be loop over three list:
+    #  - all vertex of diagram (note that for each external particle we have a vertex with a single particle attached to it)
+    #    for v in draw.vertexList:
+    #  - all vertex corresponding to the initial/final state particles
+    #    for v in draw.initial_vertex:
+    # - all the particles (initial states / final states and propagator) of the diagram
+    #    for p in draw.lineList
+    #
+    # All vertex can be assigned to a level by running
+    draw.define_level()
+    #      0: correspond to the initial state vertex
+    #      1: correspond to the T-channel level
+    #   you can use draw._debug_level() to text representation in that case
+    #   For a single line the "begin" level will always be one level lower than the "end" level
+    #    BUT for t-channel where both are equal and set to 1
+    #print(draw._debug_level())
+    #
+    # All vertex are of type VertexPoint
+    #   They have only two relevant attributes
+    #      self.lines : all the particle connecting to this vertex
+    #      self.level : level of this vertex (see above)
+    #
+    # All particles are of type FeynmanLine
+    #   They have the following relevant attributes
+    #       self.begin: vertex associated to the beginning of the particles
+    #       self.end:  vertex associated to the end of the particles
+    #       self.get('id'): pdg code
+    #       self.get('number'): number associated to the original DAG
+    #       other attributes are ['polarization', 'number', 'onshell', 'state', 'model', 'from_group', 'loop_line']
+
+    # remove all 4 point interaction
+    for v in draw.vertexList:
+        if len(v.lines) > 3:
+            return True
+        
+    # check if initial/final  states quark are emitting a gluon
+    for external in draw.initial_vertex: # vertex with only one leg for initial/final state particles
+        # external is VertexPoint object
+        p = external.lines[0] # FeynmanLine object
+        if abs(p.id) < 7: # PDG code less than 7 means a SM quark
+            other_vertex = p.end # VertexPoint object
+            if other_vertex == external:
+                other_vertex = p.begin 
+            if any(p2.id ==21 for p2 in other_vertex.lines):
+                return True      
+    return False
+
+}}}
+
+Additionally all the example below are still working but requires one more argument "model" "
+
+
+== example of user_filter.py for version of the code before 2.7.3 (not included).
+
+
 {{{
-def remove_diag(diag):
+def remove_diag(diag, model=None):
     """remove all diagram with quark in T-channel"""
     for vertex in diag['vertices']: #last
@@ -31 +104 @@
 
 {{{
-def remove_diag(diag):
+def remove_diag(diag,model=None):
     """remove all diagram which are not pure QCD or pure QED: Fake example"""
 
@@ -43 +116 @@
 import madgraph.various.misc as misc
 
-def remove_diag(diag):
+def remove_diag(diag,model=None):
     """force to have two s-channel W decaying into a specific way. 
        Designed for interference studies where decay chain are not allowed
@@ -98 +171 @@
 
 }}}
-=== 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.
-}}}