docs: public static void printMatrix(double[][] matrix)
      {
          StringBuffer sb = new StringBuffer();
          sb.append('[').append('\n');
          for ( double[] line : matrix ) {
              for ( double column : line ) {
                  sb.append(column).append(", ");
              }
              sb.append('\n');
          }
          sb.append(']');
          System.out.println(sb.toString());
      }