code: def nb_per_chunk(item_size, item_dim, chunk_size):
      
      # from Mbytes to bytes
      size = chunk_size * 10.**6
      ratio = int(round(size / (item_size*item_dim)))
      return max(10, ratio)
docs: Return the number of items that can be stored in one chunk.
  
      :param int item_size: Size of an item's scalar componant in
          Bytes (e.g. for np.float64 this is 8)
  
      :param int item_dim: Items dimension (length of the second axis)
  
      :param float chunk_size: The size of a chunk given in MBytes.