title: Appending to file using savetxt
body: <p>I'm trying to append array b and c to file.txt. The default behavior is to overwrite and I cant find any documentation on changing this.</p>
  
  <pre><code>import numpy as np
  a = np.array([1.2, 2.3, 4.5])
  b = np.array([6.7, 8.9, 10.11])
  c = np.array([12.13, 14.15, 16.17])
  
  np.savetxt('file.txt', a, fmt='%1.3f', newline=", ")
  </code></pre>
  
  <p>Thanks</p>