code: public Matrix plus(final Matrix B)
      {
          final Matrix A = this;
  
          if ((B.m_rows != A.m_rows) || (B.m_columns != A.m_columns))
          {
              throw new GeometryException("Illegal matrix dimensions");
          }
          final Matrix C = new Matrix(m_rows, m_columns);
  
          for (int i = 0; i < m_rows; i++)
          {
              for (int j = 0; j < m_columns; j++)
              {
                  C.m_data[i][j] = A.m_data[i][j] + B.m_data[i][j];
              }
          }
          return C;
      }
docs: Returns C = A + B
  
  @param B
  @return new Matrix C
  @throws GeometryException if the matrix dimensions don't match