anchor.diff:    !======================================================================!
     SUBROUTINE SUM3(N,Dsln,Diag,Indx,Temp)
       IMPLICIT NONE
  -
  +    !------
       INTEGER, INTENT(IN):: N
       INTEGER, INTENT(OUT):: Indx(*)
       DOUBLE PRECISION, INTENT(OUT):: Diag(*)
       DOUBLE PRECISION, INTENT(OUT):: Dsln(*)
       DOUBLE PRECISION, INTENT(OUT):: Temp(*)
  -
  +    !------
       INTEGER:: i
       INTEGER:: j
       INTEGER:: joc
  
positive.code: 
      joc = 0
      DO ic = Nstop, Neqns
         DO i = 1, Nstop
            Temp(i) = 0.0D0
         ENDDO
         ks = Xlnzr(ic)
         ke = Xlnzr(ic+1) - 1
         DO k = ks, ke
  
negative.code:           Temp(jj,9) = Zln(9,k)
            Indx(jj) = ic
         ENDDO
  
         DO k = ks, ke
            jj = Colno(k)
            Zln(4,k) = Temp(jj,4) - Temp(jj,1)*Diag(2,jj)
  