subroutine posten(dt) 
c 
c (* old comment Determine wkin,wmgt,wki and wenr  at time step=ne-1 
c like preenr but had an option to adjust dt. *)
c     
c     
c     I'm not sure why, it probably has something to do with variable     
c     timestep, but here grtmx is recalculated.
c     
c
      implicit none 
      include 'itg.par' 
      include 'itg.cmn' 
c 
      real den2m(mz,nz),v2m(mz,nz),tpar2m(mz,nz),tp2m(mz,nz)
      real u2(mz,nz),edif,etot,dt(mz),dum
      real den2,v2,tpar2,tp2,wenrn,dedt,dt1
      integer m,n 
c 
      call volsq(potential,potential,dum,u2)

      if(ncycle.gt.2) then 
         do n=1,nd 
            do m=1,md
               edif=u2(m,n)-grtmx(ne,m,n)
               etot=u2(m,n)+grtmx(ne,m,n)
               if (abs(etot).lt.1.0e-33) then 
                  grtmx(ne,m,n) = 0.0 
               else
                  grtmx(ne,m,n)=edif/(2.*dt(m)*etot) 
               endif 
            enddo
         enddo
      else 
         do n=1,nd 
            do m=1,md 
               grtmx(ne,m,n)=0.0 
            enddo
         enddo
      endif 
c
c
c     calculate energy conservation, 2nd order accurate in dt
c     
      call volsq(density,density,den2,den2m)
      call volsq(u_par,u_par,v2,v2m)
      call volsq(t_par,t_par,tpar2,tpar2m)
      call volsq(t_perp,t_perp,tp2,tp2m)
c
c Without subcycling, this calculation only makes sense if all modes are 
c being advanced with the same time step.  It is not vital in the 
c linear cases, so replace dt with dt(md) as elsewhere:
c
      dt1=dt(md)
      wenrn=0.5*(den2+v2+tpar2/2.+tp2)
      dedt=(dt1/dtold*(wenr-pwenr)
     .     +dtold/dt1*(wenrn-wenr))/(dt1+dtold)
      if(wenrn.ne.0.) then
         pcerr(ne)=(dedt-drive)/wenrn
      else
         pcerr(ne)=0.
      endif

      return
      end