Building a multi-dimensional array of variables
The next step in our example (after creating an empty Model
object) is to add decision variables to the model. The variables are created
using addVars, and are returned in a tupledict which
we'll call flow:
# Create optimization model
m = gp.Model('netflow')
# Create variables
flow = m.addVars(commodities, arcs, obj=cost, name="flow")
The first, positional arguments to addVars give the index set.
In this case, we'll be indexing flow by commodities and
arcs. In other words, flow[c,i,j] will capture the flow
of commodity c from node i to node j. Note that
flow only contains variables for source, destination pairs
that are present in arcs.
Note also that flow[c,i,j] is a continuous decision variable;
variables are assumed to be continuous unless you state otherwise.
