title: Error with Padlen in signal.filtfilt in Python
body: <p>I am working with library "scipy.signal" in Python and I have the next code:</p>
  
  <pre><code>from scipy import signal
  
  b = [ 0.001016    0.00507999  0.01015998  0.01015998  0.00507999  0.001016  ]
  
  a = [ 1.         -3.0820186   4.04351697 -2.76126457  0.97291013 -0.14063199]
  data = [[ 1.]
  [ 1.]
  [ 1.]
  ...]
  # length = 264
  y = signal.filtfilt(b, a, data)
  </code></pre>
  
  <p>But when I execute the code I get the next error message:</p>
  
  <pre><code>The length of the input vector x must be at least padlen, which is 18.
  </code></pre>
  
  <p>What could I do?</p>