code: public Matrix removeColumn(int j) {
          if (j >= columns || j < 0) {
              throw new IndexOutOfBoundsException("Illegal column number, must be 0.." + (columns - 1));
          }
  
          Matrix result = blankOfShape(rows, columns - 1);
  
          for (int jj = 0; jj < j; jj++) {
              result.setColumn(jj, getColumn(jj));
          }
  
          for (int jj = j + 1; jj < columns; jj++) {
              result.setColumn(jj - 1, getColumn(jj));
          }
  
          return result;
      }
docs: Removes one column from matrix.
  @param j the column index
  @return matrix without column.