Method operator-

inst/include/Rcpp/vector/MatrixBase.h:131–133

                return iterator( object, i + (j*nr) + n ) ;
            }
            inline iterator operator-(difference_type n) const {
                return iterator( object, i + (j*nr) - n ) ;
            }

            inline iterator& operator+=(difference_type n) {
                update_index( i + j*nr + n );