parameter (nxx=361,nyx=361)
      dimension t1(0:nxx,0:nyx),t2(0:nxx,0:nyx),t3(0:nxx,0:nyx),t4(0:nxx,0:nyx)
      dimension ftm(nxx,nyx),ftp(nxx,nyx),flux(nxx,nyx)

      logical iperx

      common /topo/ iperx