title: Constraint of an unknown type passed to function
body: <p>Hi I am doing a minimization problem and I wanted to try the <code>'trust-constr'</code> method, with scipy function <code>optimize.minimize</code>, to compare it with the 'SLSQP' results. Unfortunatly I don't know why when I set my method to <code>'trust-constr'</code>, it tells me that :</p>
  
  <p>ValueError: <code>constraint</code> of an unknown type is passed.</p>
  
  <p>The code is the following:</p>
  
  <pre><code>con1 = {'type':'eq', 'fun': eq2}
  con2 =  {'type':'ineq', 'fun' : ieq_bck2}
  con3 =  {'type':'ineq', 'fun' : ineq_rb2}
  con4 =  {'type':'ineq', 'fun' : ls2}
  
  con = ([con1, con2, con3, con4])
  
  scipy.optimize.minimize(fitness2, opt, method = 'trust-constr', jac = 
  'cs', hess = h1, constraints = con)
  </code></pre>
  
  <p>Any idea of how to solve it?</p>