Class DiagramTag

source code

object --+
         |
        DiagramTag

Known Subclasses:

• iolibs.group_subprocs.IdentifyConfigTag
• , helas_objects.IdentifyMETag
• , various.diagram_symmetry.IdentifySGConfigTag

Class to tag diagrams based on objects with some __lt__ measure, e.g.
PDG code/interaction id (for comparing diagrams from the same amplitude),
or Lorentz/coupling/mass/width (for comparing AMPs from different MEs).
Algorithm: Create chains starting from external particles:
1 \        / 6
2 /\______/\ 7
3_ /  |   \_ 8
4 /   5    \_ 9
            \ 10
gives ((((9,10,id910),8,id9108),(6,7,id67),id910867)
       (((1,2,id12),(3,4,id34)),id1234),
       5,id91086712345)
where idN is the id of the corresponding interaction. The ordering within
chains is based on chain length (depth; here, 1234 has depth 2, 910867 has
depth 3, 5 has depht 0), and if equal on the ordering of the chain elements.
The determination of central vertex is based on minimizing the chain length
for the longest subchain. 
This gives a unique tag which can be used to identify diagrams
(instead of symmetry), as well as identify identical matrix elements from
different processes.