title: product of two variable in Google Optimization Tools python
body: <p>I have a optimization problem. The object is to max two variable x and y. How to represent it in google optimization tools python version.</p>
  
  <p>what i can do  now is:</p>
  
  <pre><code> from ortools.linear_solver import pywraplp
   solver = pywraplp.Solver('RunIntegerExampleCppStyleAPI',pywraplp.Solver.CBC_MIXED_INTEGER_PROGRAMMING)
   x=solver.IntVar(0, 1, 'x')
   y=solver.Intvar(0,1,'y')
   objective = solver.Objective()
   #so how to get the object function of max x*y?
  </code></pre>