anchor.diff:  
     call solvent% random_placement(solvent_cells% edges, colloids, solvent_colloid_lj)
   
  +  do i=1, solvent% Nmax
  +     solvent% vel(1,i) = threefry_normal(state(1))*sqrt(T) + max_speed*solvent% pos(3,i)*(L(3) - solvent% pos(3,i))/(L(3)/2)**2
  +     solvent% vel(2,i) = threefry_normal(state(1))*sqrt(T)
  +     solvent% vel(3,i) = threefry_normal(state(1))*sqrt(T)
  +  end do
  +
     do m = 1, solvent% Nmax
        if (solvent% pos(2,m) < (L(2)/2.d0)) then
           solvent% species(m) = 1
  
positive.code: 
    double precision :: g(3) !gravity
    logical :: fixed, on_track, stopped,order
    integer :: bufferlength
    integer :: steps_fixed
    fixed = .true.
    on_track = .true.
  
negative.code:   shift = max(sigma_C, sigma_N)*2**(1./6.) + 0.25
    call walls_colloid_lj% init(epsilon(1:1,:), sigma(1:1,:), sigma_cut(1:1,:), shift)
    write(*,*) epsilon(1:2,:), sigma(1:2,:), sigma_cut(1:2,:), shift
    
  
    mass(1) = rho * sigma_C**3 * 4 * 3.14159265/3
    mass(2) = rho * sigma_N**3 * 4 * 3.14159265/3
  