Constrains the sum of the elements in Collection to satisfy the relation sum(Collection) Rel Sum.
Rel can be one of #>, #>=, #<, #=<, #=, #\= (or equivalently, >, >=, <, =<, =, \=).
Any input variables which are not already domain variable will be turn into domain variables with default bounds.
You may find it more convenient to embed sum(Collections,RelOp) in a constraint expression.
ConsistencyModule is the optional module specification to give the consistency level for the propagation for this constraint: gfd_bc for bounds consistency, and gfd_gac for domain (generalised arc) consistency.
Domain consistency is different from bounds consistency only if Rel is #=.
This constraint is known as sum_ctr in the global constraint catalog, and is implemented using Gecode's linear() constraint.