anchor.diff:             end if
           end if
   
  +        if (modulo(j, colloid_sampling) == 0) then
  +           call dimer_io%position%append(colloids%pos)
  +           call dimer_io%velocity%append(colloids%vel)
  +           call dimer_io%image%append(colloids%image)
  +        end if
  +
        end do md_loop
   
        call random_number(solvent_cells% origin)
  
positive.code: !! \param tau              MPCD collision time
  !! \param N_MD_steps       number MD steps occuring in tau
  !! \param N_loop           number of MPCD timesteps
  !! \param steps_fixed      number of steps during which the colloid is fixed
  !! \param sigma_C          radius of C sphere
  !! \param sigma_N          radius of N sphere
  
negative.code:      call catalytic_change_el%append(catalytic_change)
       call bulk_change_el%append(bulk_change)
  
       call h5fflush_f(hfile%id, H5F_SCOPE_GLOBAL_F, error)
  
       if (fixed) then
  