anchor.diff:              model%F => u
               model%dF => du
               model%d2F => d2u
  +            model%dF_inv => du_inv
               model%Gamma => Gamma
               model%dGamma => dGamma
               model%beta = beta
  
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: 
          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
  