code: public Matrix add(Matrix m) throws MatrixException
      {
          // Validate m's size.
          if ((nRows != m.nRows) && (nCols != m.nCols)) {
              throw new MatrixException(
                                  MatrixException.INVALID_DIMENSIONS);
          }
  
          double sv[][] = new double[nRows][nCols]; // sum values
  
          // Compute values of the sum.
          for (int r = 0; r < nRows; ++r) {
              for (int c = 0; c < nCols; ++c) {
                  sv[r][c] = values[r][c] + m.values[r][c];
              }
          }
  
          return new Matrix(sv);
      }
docs: Add another matrix to this matrix.
  @param m the matrix addend
  @return the sum matrix
  @throws numbercruncher.MatrixException for invalid size