subroutine entro(s,u,ar,sflux)
c
      implicit none
      include 'itg.par'
c
      real s(lz,mz,nz,nspecz),u(lz,mz,nz,nspecz),
     * ar(mz,nz),sflux,coef
      integer l,m,n,mr
c
      include 'itg.cmn'
c
c    normalize by pi*y0 in the x-direction
c
      sflux=0.0
      coef=0.25/(pi*y0)
c
      do 10 n=1,nd
      do 10 m=1,md
      mr=mrr(m,n)
      ar(m,n)=0.5*(mr/y0)*u(1,m,n,1)*s(1,m,n,1)*dr(1)
      do 20 l=2,ldb
      ar(m,n)=ar(m,n)+(mr/y0)*u(l,m,n,1)*s(l,m,n,1)*dr(l)
   20 continue
      ar(m,n)=ar(m,n)+0.5*(mr/y0)*u(ld,m,n,1)*s(ld,m,n,1)*dr(ld)
      ar(m,n)=coef*ar(m,n)
      sflux=sflux+ar(m,n)
   10 continue
c
      return
      end