# setting default LP solver

I installed Gurobi, and have gotten Sage to recognize it. So when I use a command such as vertex_coloring(G,solver="GUROBI") everything works fine.

But what if I want to use instead a command such as G.chromatic_number(algorithm="MILP"). How do I make sure that the LP solver that Sage is using is Gurobi, rather than GLPK? Is there one place I can tell Sage that it should always default to Gurobi as its LP solver, or is it possible that Sage is smart enough that once Gurobi is installed it does that anyway?

(Also, peripherally: does anyone have any idea whether chromatic_number or vertex_coloring is more efficient for large graphs?)

About your comment on coloring algorithms: it heavily depend on the LP solver that you use, and then it depends on the graphs themselves.