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