title: How to form a matrix from submatrices?
body: <p>Let's say that I have these 4 submatrices:</p>
  
  <pre><code>print(A[0])
  print(A[1])
  print(A[2])
  print(A[3])
  
  [[  0.   1.   2.]
   [  6.   7.   8.]
   [ 12.  13.  14.]]
  [[  3.   4.   5.]
   [  9.  10.  11.]
   [ 15.  16.  17.]]
  [[ 18.  19.  20.]
   [ 24.  25.  26.]
   [ 30.  31.  32.]]
  [[ 21.  22.  23.]
   [ 27.  28.  29.]
   [ 33.  34.  35.]]
  </code></pre>
  
  <p>From this matrix:</p>
  
  <pre><code>[[ 0  1  2  3  4  5]
   [ 6  7  8  9 10 11]
   [12 13 14 15 16 17]
   [18 19 20 21 22 23]
   [24 25 26 27 28 29]
   [30 31 32 33 34 35]]
  </code></pre>
  
  <p>How can I manage the submatrix to reproduce the original one?</p>