anchor.diff:            id(1) = j1
             id(2) = j2
             id(3) = j3
  -          id(4) = j4
  -          ia = id(4)+jd(4)*(id(3)-1+jd(3)*(id(2)-1+jd(2)*(id(1)-1)))
  +          !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(l)+jd(l)*(id(k)-1+jd(k)*(id(j)-1+jd(j)*(id(i)-1)))
             s(ib) = u(ia) * factor
            enddo
  
positive.code:         do j2 = 1,b
           do j4 = 1,d
            id(1) = j1
            id(2) = j2
            id(3) = j3
            id(4) = j4
            ia = id(4)+jd(4)*(id(3)-1+jd(3)*(id(2)-1+jd(2)*(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
         enddo
        enddo
        else
        do j2 = 1,b
         do j3 = 1,c
          do j1 = 1,a
           do j4 = 1,d
            id(1) = j1
            id(2) = j2
            id(3) = j3
            id(4) = j4
            ia = id(4)+jd(4)*(id(3)-1+jd(3)*(id(2)-1+jd(2)*(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
  
negative.code:          do j4 = 1,d
            id(1) = j1
            id(2) = j2
            !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
  