title: Gurobi Python - Add certain vars
body: <p>I'm new to Gurobi and I'd like to know how to add certain variables to a model. For example, if I have an uncomplete graph, I'd like to add a variable x[i,j] for each arc of the graph. I don't want to add all the arcs of the complete graph, because it has a huge number of nodes and my computer runs out of memory. So I'm trying to avoid defining variables with lists for it's indexes.</p>
  
  <p>Thanks in advance, </p>