anchor.diff:    close(15)
   
     call compute_variables(s)
  +  call timestep (s,dt_T, dt_nu)
   
     ! Open unit 13 to write
     ! do it more safely
  
positive.code:           prev_S = s%S
            
            ! Integrate S
            call do_timestep_S(s, dt_nu)
            
            ! Increment time, number of iterations
            t = t + dt_nu
            iteration = iteration + 1
            ! Output things here
            if (mod(iteration, output_freq) == 0) then
  
negative.code:   !use mod_s_curve
    use mod_integrator
    use mod_output
    use mod_timestep
  
    implicit none
  
  