subroutine arrows(u,conddat,ncond,coeg,itri,nno,
     $     nrtri,nelgrp,arrow,amass)
      implicit double precision (a-h,o-z)
      dimension conddat(ncond,*),u(*),coeg(2,*),itri(4,*)
      dimension arrow(2,*),amass(*),nelgrp(5,*)
      dimension xc(3),yc(3),condu(2,2)
      character*80 rhscha,cndcha(3),cnvcha(2),abscha,ex
*
      common /chardata/ idrhs,idcnd,idcnv,idabs,
     $     rhscha,cndcha,cnvcha,abscha
*
      do 20 iel=1,nrtri
         xm=0.d0
         ym=0.d0
         do 15 j=1,3
            ivj=itri(j,iel)
            xc(j)=coeg(1,ivj)
            yc(j)=coeg(2,ivj)
            xm=xm+xc(j)/3.d0
            ym=ym+yc(j)/3.d0
15       continue
*
*********************************************************
*         conduction 
*********************************************************
*
         do i=1,2
            do j=1,2
               condu(i,j)=0.d0
            enddo
         enddo
*
         if(idcnd.eq.0) then
            ex=cndcha(1)
            call evalexpr(ex, xm, ym, c1, ierr)
            condu(1,1)=c1
            ex=cndcha(2)
            call evalexpr(ex, xm, ym, c1, ierr)
            condu(1,2)=c1
            ex=cndcha(3)
            call evalexpr(ex, xm, ym, c1, ierr)
            condu(2,2)=c1
           condu(2,1)=condu(1,2)
         endif
         if(idcnd.eq.1) then
            call shepardv(
     i           xm,ym,ncond,conddat(1,1),conddat(1,2),conddat(1,3),3,
     o           condu(1,1))
            condu(2,2)=condu(1,2)
            condu(1,2)=condu(2,1)
         endif
         if(idcnd.eq.2) then
            ielfa=macrotr(iel,itri,nelgrp)
            condu(1,1)=conddat(1,ielfa)
            condu(2,1)=conddat(2,ielfa)
            condu(1,2)=condu(2,1)
            condu(2,2)=conddat(3,ielfa)
         endif
*
         call grad(ux,uy,coeg,u,itri(1,iel))
         uxm = - condu(1,1)*ux - condu(1,2)*uy
         uym = - condu(2,1)*ux - condu(2,2)*uy
         da = tarea(xc,yc)
         do 16 j=1,3
            ivj=itri(j,iel)
            arrow(1,ivj)=arrow(1,ivj)+da*uxm
            arrow(2,ivj)=arrow(2,ivj)+da*uym
            amass(ivj)=amass(ivj)+da
16       continue
20       continue
         do 30 j=1,nno
            if(amass(j).eq.0.d0) goto 30
            arrow(1,j)=arrow(1,j)/amass(j)
            arrow(2,j)=arrow(2,j)/amass(j)
30       continue
*
      return
      end