anchor.diff:    dt = tau / N_MD_steps
     N_loop = PTread_i(config, 'N_loop')
     N_therm = PTread_i(config, 'N_therm')
  +  vxz_interval = PTread(config, 'vxz_interval')
   
     wall_t = PTread_dvec(config, 'wall_T', 2)
     T = PTread_d(config, 'T')
  
positive.code:   type(profile_t) :: vx
    type(h5md_element_t) :: elem_tz, elem_tz_count
    type(h5md_element_t) :: elem_rhoz
    double precision, allocatable :: v_xz(:,:,:)
    integer, allocatable :: v_xz_count(:,:)
    type(h5md_element_t) :: v_xz_el
  
    integer :: rho
  
negative.code:   double precision :: tau, dt , T, alpha
    double precision :: skin, co_max, so_max
    integer :: N_MD_steps, N_loop
    integer :: vxz_interval
    integer :: N_therm
    integer :: n_extra_sorting
    double precision :: kin_e, temperature
  