title: Understanding scipy nnls output
body: <p>I want to understand the output from nnls in scipy:
  The code is:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from scipy.optimize import nnls
  A = np.array([[30, 120, 90],[60, 90, 120]])
  b = np.array([67.5, 60])
  x, rnorm = nnls(A,b)
  print x, rnorm
  </code></pre>
  
  <h1>Output is:</h1>
  
  <h1>[ 0.          0.42857143  0.17857143] 0.0</h1>