title: How to convert a column or row matrix to a diagonal matrix in Python?
body: <p>I have a row vector A, A = [a1 a2 a3 ..... an] and I would like to create a diagonal matrix, B = diag(a1, a2, a3, ....., an) with the elements of this row vector. How can this be done in Python?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>This is the code to illustrate the problem:</p>
  
  <pre><code>import numpy as np
  a = np.matrix([1,2,3,4])
  d = np.diag(a)
  print (d)
  </code></pre>
  
  <p>the output of this code is [1], but my desired output is:</p>
  
  <pre><code>[[1 0 0 0]
   [0 2 0 0]
   [0 0 3 0]
   [0 0 0 4]]
  </code></pre>