anchor.diff:        DO I = 1, NX
          XI = X(I,:)
          DO J = 1, N
  -        B(I,J) = BIJ(XI, XNODE(NODOFEL(N,J,1),:), XNODE(NODOFEL(N,J,2),:))
  -        C(I,J) = CIJ(XI, XNODE(NODOFEL(N,J,1),:), XNODE(NODOFEL(N,J,2),:))
  +        CALL BCIJ(XI, XNODE(NODOFEL(N,J,1),:), XNODE(NODOFEL(N,J,2),:), BIJ, CIJ)
  +        B(I,J) = BIJ
  +        C(I,J) = CIJ
          END DO
         END DO
   END SUBROUTINE
  
positive.code: SUBROUTINE BCONDVEL(N, XNODE, U, CHI)
        IMPLICIT NONE
        INTEGER, INTENT(IN) :: N
        REAL, DIMENSION(N,2), INTENT(IN) :: XNODE
        REAL, DIMENSION(2), INTENT(IN) :: U
        REAL, DIMENSION(N), INTENT(OUT) :: CHI
        REAL, DIMENSION(2) :: T
        INTEGER :: I, NODOFEL
        DO I = 1, N
         T = XNODE(NODOFEL(N,I,2),:) - XNODE(NODOFEL(N,I,1),:)
         T = T/SQRT(T(1)**2 + T(2)**2)
         CHI(I) = U(1)*T(2) - U(2)*T(1)
        END DO
  
negative.code:       IMPLICIT NONE
        INTEGER, INTENT(IN) :: NX, N
        REAL, DIMENSION(NX,2), INTENT(IN) :: X
        REAL, DIMENSION(N,3), INTENT(IN) :: XNODE
        REAL, DIMENSION(NX,N), INTENT(OUT) :: B, C
        REAL, DIMENSION(2) :: XI
        REAL :: BIJ, CIJ
  