anchor.diff:            id(3) = j3
             id(4) = j4
             ia = id(4)+d*(id(3)-1+c*(id(2)-1+b*(id(1)-1)))
  -          ib = id(l)+jd(l)*(id(k)-1+jd(k)*(id(j)-1+jd(j)*(id(i)-1)))
  +          ib = id(2)+jd(2)*(id(k)-1+jd(k)*(id(j)-1+jd(j)*(id(i)-1)))
             s(ib) = u(ia) * factor
            enddo
           enddo
  
positive.code:           id(3) = j3
            id(4) = j4
            ia = id(4)+d*(id(3)-1+c*(id(2)-1+b*(id(1)-1)))
            ib = id(l)+jd(l)*(id(k)-1+jd(k)*(id(j)-1+jd(j)*(id(i)-1)))
            s(ib) = u(ia) * factor
           enddo
          enddo
  
negative.code:           id(3) = j3
            !id(4) = j4 ! 1234 are only used once and we know l=4, hence ijk must not be 4
            ia = id(4)+d*(id(3)-1+c*(id(2)-1+b*(id(1)-1)))
            ib = id(4)+jd(4)*(id(k)-1+jd(k)*(id(j)-1+jd(j)*(id(i)-1)))
            s(ib) = u(ia) * factor
           enddo
          enddo
  