Container separation

Assuming you have got binary variables ifuse(i,j) that indicate whether an arc is used, you could associate variables for the container selection with these as follows:

declarations

  Plants: range

  Suppliers = {"L1","L2","L3"}

  Containers = 1..6

  ifuse: dynamic array(Suppliers,Plants) of mpvar

  assign: dynamic array(Containers,Suppliers,Plants) of mpvar

end-declarations

!... create variables 'ifuse' ...

forall(c in Containers, i in Suppliers,j in Plants | exists(ifuse(i,j))) do

   create(assign(c,i,j))

   assign(c,i,j) is_binary

end-do

! Use container on at most one arc

forall(c in Containers)

  sum(i in Suppliers,j in Plants | exists(assign(c,i,j))) assign(c,i,j)<=1

! If arc is used, assign at least one container to it

forall(i in Suppliers,j in Plants | exists(ifuse(i,j)))

   ifuse(i,j) <= sum(c in Containers) assign(c,i,j)

! Only assign containers to arcs that are used

forall(c in Containers, i in Suppliers,j in Plants | exists(assign(c,i,j)))

   assign(c,i,j) <= ifuse(i,j)

You might want to try adding some additional constraints for breaking symmetry if all containers are equivalent, for example:

forall(c in Containers | c>1) do

   ct:=1

   sum(ct as counter, i in Suppliers,j in Plants | exists(ifuse(i,j)))

    ct*(assign(c-1,i,j) - assign(c,i,j)) <= 0

end-do