code: double[] getBlockData(int row, int column) {
  		int blockNumber = layout.getBlockNumber(row, column);
  		double[] block = data[blockNumber];
  
  		if (null == block) {
  			block = new double[layout.getBlockSize(row, column)];
  			data[blockNumber] = block;
  		}
  		return data[blockNumber];
  	}
docs: Get block holding the specified row and column. If none exist, create
  one.
  
  @param row
  - in matrix
  @param column
  - in matrix
  @return double[] block where the given row,column is held.