anchor.diff:         converge = .false.
       end if
   
  -    ! Copy the result
     end subroutine do_timestep_T
   
   end module mod_integrator
  
positive.code:     call compute_variables(s)
      ! Let dT/dt = f0 and d²T/dt² = f1 so T(t+1) = T(t) + dt * f0 * (1 + dt * f1)
  
      f0 = f(s)
      fT = (f(s_deriv) - f0) / dtemp
  
      rhs = f0 / fT * (exp(fT*dt) - 1._x_precision)
      ! rhs = dt*f0 * (1._x_precision + 0.5_x_precision*dt*fT)
  
negative.code:     diag_low = -s%nu(1:n_cell-1) / x2(2:  n_cell) * dtoverdx2
  
      diag(n_cell)       = 1 + s%nu(n_cell) / x2(n_cell) * dtoverdx2
      diag_low(n_cell-1) = - s%nu(n_cell-1) / x2(n_cell) * dtoverdx2
  
      s%S(n_cell) = s%S(n_cell) + dt * overdx / x2(n_cell)
  
  