code: @Override
      public BandMatrix transpose() {
          BandMatrix at = new BandMatrix(n, m2, m1);
          for (int i = 0; i < n; i++) {
              for (int j = i-m2; j <= i+m1; j++) {
                  if (j >= 0 && j < n) {
                      at.set(i, j, get(j, i));
                  }
              }
          }
  
          return at;
      }
docs: Returns the matrix transpose.
  @return the transpose of matrix.