title: scipy.optimize with non linear constraints
body: <p>I have non-linear function with non-linear constraints and I'd like to optimize it. I don't know how to define non-linear constraints using scipy.optimize. My code so far looks like:</p>
  
  <pre><code>from math import cos, atan
  import numpy as np
  from scipy.optimize import minimize
  import sympy as sy
  
  def f(x):
      return 0.1*x*y
  
  def ineq_constraint(x):
      x**2 + y**2 - (5+2.2*sy.cos(10*sy.atan(x/y)))**2
      return x,y
  
  con = {'type': 'ineq', 'fun': ineq_constraint}
  minimize(f,x0,method='SLSQP',constraints=con)
  </code></pre>