title: How to calculate RMSE using IPython/NumPy?
body: <p>I'm having issues trying to calculate root mean squared error in IPython using NumPy. I'm pretty sure the function is right, but when I try and input values, it gives me the following TypeError message:</p>
  
  <pre><code>TypeError: unsupported operand type(s) for -: 'tuple' and 'tuple'
  </code></pre>
  
  <p>Here's my code:</p>
  
  <pre><code>import numpy as np
  
  def rmse(predictions, targets):
      return np.sqrt(((predictions - targets) ** 2).mean())
  
  print rmse((2,2,3),(0,2,6))
  </code></pre>
  
  <p>Obviously something is wrong with my inputs. Do I need to establish the array before I put it in the <code>rmse():</code> line?</p>