Merged requested to merge seitz/pystencils:sum-prod into master
Sum and Product have a indexing variable which is a Atom but not a free
symbol. So logic, that defines the undefined symbols in a
SympyAssignment should not be
sp.Indexed from the
ResolvedFieldAcesses forms an edge case.
So we could also use
I hope I extracted from my fork all the necessary code to implement this feature.