def add_variable(var)
      ret = Gurobi.GRBaddvar @ptr, 0, nil, nil, var.coefficient,
                             var.lower_bound, var.upper_bound,
                             gurobi_type(var.type), var.name
      fail if ret != 0

      store_variable var
    end
def add_variable(var)
      ret = Gurobi.GRBaddvar @ptr, 0, nil, nil, var.coefficient,
                             var.lower_bound, var.upper_bound,
                             gurobi_type(var.type), var.name
      fail if ret != 0

      store_variable var
    end
Add a new variable to the model