Hi,   There are multiple ways of modeling this. One is to add a new constraint on the outflow of the nodes (i.e. the sum over all DC and commodities from farm a must be less than the total capacity)   To achieve this with the code in the example I have changed the supply_data dataset by adding all nodes (i.e. add the DCs here) and adding an extra variable indicating the max flow through the node. In the optmodel  code I have added a new "num" statement to hold the new capacity data and added it to the 'read data' statement. Finally, I've added a new constraint 'flow_cap' that sums over all flow out of a node (the constraint is defined over all nodes 'i' but the sum is only done over the arcs that start in 'i').   I've attached the modified program. With the data I've added you should see the overall (flow) capacity constraints on farm b and through the Chicago DC kick in and make the overall optmial flow more expensive  ... View more