anchor.diff:  
     L = PTread_ivec(config, 'L', 3, loc=params_group)
     rho = PTread_i(config, 'rho', loc=params_group)
  -  N = rho *L(1)*L(2)*L(3)
   
     T = PTread_d(config, 'T', loc=params_group)
     link_d = PTread_dvec(config, 'link_d', 2, loc=params_group)
  
positive.code: 
    sigma_E = PTread_d(config, 'sigma_E', loc=params_group)
    sigma_N = PTread_d(config, 'sigma_N', loc=params_group)
  
    ! solvent index first, colloid index second, in solvent_colloid_lj
    epsilon(:,1) = PTread_dvec(config, 'epsilon_E', 3, loc=params_group)
  
negative.code:   colloids% force_old = colloids% force
  
    call h5fflush_f(hfile%id, H5F_SCOPE_GLOBAL_F, error)
  
    write(*,*) 'Box size', L
    write(*,*) N, 'fluid particles'
  
    write(*,*) 'Running for', equilibration_loops, '+', N_loop, 'loops'
  
    call main%tic()
  