title: Minimize System of Equations with constraints (scipy.optimize.minimize)
body: <p>Consider the following code:</p>
  <pre><code>import numpy as np
  from scipy.optimize import minimize
  
  def eq( p ):
      s1,s2,s3 = p 
      f1 = 1.1**3 / s1*1.1**1+s2*1.1**2+s3*1.1**3
      f2 = 0.9**1 / s1*0.9**1+s2*0.9**2+s3*0.9**3
      return (f1, f2) 
  
  bnds = ( (0, None), (0, None), (0, None) )
  cons = ( { 'type' : 'ineq', 'fun': lambda p: p[0]+p[1]+p[2] - 1} )
  
  
  minimize( eq, (0.3,0.3,0.3),  bounds=bnds, constraints=cons )
  </code></pre>
  <p>throws the error</p>
  <pre><code>TypeError: unsupported operand type(s) for -: 'tuple' and 'tuple'
  </code></pre>
  <p>I want to minimize <code>f1</code> and <code>f2</code> such that the <code>s_t &gt; 0</code> and <code>sum s_t &lt;= 1</code>, for t = 1, 2, 3.</p>