anchor.diff:    !start RMPCDMD
     setup: do i = 1, N_loop
        if (modulo(i,20) == 0) write(*,'(i09)',advance='no') i
  -     md: do j = 1, N_MD_steps
  +     md_loop: do j = 1, N_MD_steps
           call mpcd_stream_zwall_light(solvent, solvent_cells, dt,g)
   
           colloids% pos_rattle = colloids% pos
  
positive.code:            call change_timer%tac()
          end if
  
       end do md
  
       
  
  
negative.code:           theta = atan(solvent_pos(2,o)/solvent_pos(1,o))
            solvent_pos(1,o) = r
            solvent_pos(2,o) = theta
            if ((solvent_pos(1,o) < 2*max_cut).and.(solvent_pos(3,o)<1.5d0*d).and.(solvent_pos(3,o)>-0.5d0*d)) then
               if (solvent% species(o)==2) then
                  check = floor((solvent_pos(3,o)+0.5d0*d)/dz)
                  check = check+1 
                  conc_z_cyl(check) = conc_z_cyl(check) + 1
               end if
            end if 
  