code: public void eachInColumn(int j, VectorProcedure procedure) {
          VectorIterator it = iteratorOfColumn(j);
  
          while (it.hasNext()) {
              double x = it.next();
              int i = it.index();
              procedure.apply(i, x);
          }
      }
docs: Applies given {@code procedure} to each element of specified column of this matrix.
  
  @param j the column index
  @param procedure the vector procedure