title: Issue with integer optimization with Gekko
body: <p>I tried with this code and the result was <code>(2,2)</code>. Obviously it's not true, since <code>(0,4)</code> is a best solution. could you please tell me where is it the problem?</p>
  <pre><code>import numpy as np
  from gekko import GEKKO
  m = GEKKO()
  
  x=[m.Var(lb=0,ub=4,integer=True) for i in range(2)]
  
  m.options.SOLVER = 1
  
  #Equations
  
  m.Equation(m.sum(x)&gt;=4)
  
  #Objective
  
  m.Obj(x[0]*x[1])
  m.solve(disp=False)
  print(x[0].value)
  print(x[1].value)
  </code></pre>