anchor.diff:            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).or.(solvent_pos(3,o)>-0.5d0*d))) then
  +          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 
  
positive.code:         fixed = .false.
       end if
       if (.not. on_track) then
          if (modulo(i,50)==0) then
             call concentration_field_cylindrical
             write(18,*) conc_z, colloid_pos
           end if
  
negative.code:   !start RMPCDMD
    setup: do i = 1, N_loop
       if (modulo(i,20) == 0) write(*,'(i09)',advance='no') i
       md_loop: do j = 1, N_MD_steps
          call mpcd_stream_zwall_light(solvent, solvent_cells, dt,g)
  
          colloids% pos_rattle = colloids% pos
  