anchor.diff:  
           end function du
   
  +        function du_inv(mret,d,s,z)
  +            real(dp), intent(in)                :: mret,d,s,z
  +            real(dp)                            :: du_inv
  +
  +            du_inv = (1/mret)**(1/tau)
  +        end function du_inv
  +
           function d2u(c,d,s,z)
               real(dp), dimension(:), intent(in)  :: c
               real(dp), intent(in)                :: d,s,z
  
positive.code:     use kinds, only: dp
      use ncegm, only: ncegm_setup, ncegm_solve, ncegm_model, ncegm_getPolicy_c, ncegm_getPolicy_d, ncegm_getValueFunction, ncegm_getPolicy_aprime
      use grids, only: build_grid
      private
      public :: start_demo_blc
      save
  
negative.code:             model%F => u
              model%dF => du
              model%d2F => d2u
              model%dF_inv => du_inv
              model%Gamma => Gamma
              model%dGamma => dGamma
              model%beta = beta
  