subroutine tangen(n,ta,vf,curv,ut,tauf,sl,pei,flt,dcut)
*     ************************************************************
*     obtain the tangential velocity
*     ************************************************************
      integer n,j
      double precision ta(0:8192),vf(0:8192),curv(0:8192)
      double precision ut(0:8192),tauf(0:8192)
      double precision flt,h,hp,pi,p2,sl,pei,vn,dcut
      common/gridsz/h,hp
      common/valupi/pi,p2

      do 20 j=0,n
         vn = vf(j) - sl*dexp(-pei*curv(j))
         tauf(j) = vn*ta(j)
 20   continue

      call fin2(n,h,p2,ut,tauf)

      flt = ut(n)

      do 30 j=0,n
         ut(j) = ut(j) - dfloat(j)*h*flt
 30   continue

      do 40 j=0,n
         tauf(j) = ta(j)*ut(j)
 40   continue

      call kfilter(n,dcut,tauf)

      call fast(tauf,n)

      end