anchor.diff:       call dimer_io%velocity%append(colloids%vel)
        call dimer_io%image%append(colloids%image)
   
  -     if (i .gt. 2000) then
  +     if (i >= steps_fixed) then
           fixed = .false.
        end if
        
  
positive.code:   double precision :: g(3) !gravity
    logical :: fixed, on_track, stopped, order
    integer :: bufferlength
    fixed = .true.
    on_track = .true.
    stopped = .false.
  
negative.code:   N_MD_steps = PTread_i(config, 'N_MD')
    dt = tau / N_MD_steps
    N_loop = PTread_i(config, 'N_loop')
    steps_fixed = PTread_i(config, 'steps_fixed')
    
    sigma_C = PTread_d(config, 'sigma_C')
    sigma_N = PTread_d(config, 'sigma_N')
  