anchor.diff:          type(qmc_in_t) :: qmc_in
           type(restart_in_t) :: restart_in
           type(reference_t) :: reference
  -
  -        integer :: opts
  -        character(10), parameter :: keys(4) = [character(10) :: 'sys', 'qmc', 'restart', 'reference']
  +        logical :: use_sparse_hamil
  +
  +        integer :: opts, err
  +        character(12), parameter :: keys(5) = [character(12) :: 'sys', 'qmc', 'restart', 'reference', 'sparse_hamil']
   
           lua_state = flu_copyptr(L)
           call get_sys_t(lua_state, sys)
  
positive.code:         call read_qmc_in(lua_state, opts, qmc_in, .true.)
          call read_restart_in(lua_state, opts, restart_in)
          call read_reference_t(lua_state, opts, sys, reference)
          call warn_unused_args(lua_state, keys, opts)
          call aot_table_close(lua_state, opts)
  
          calc_type = simple_fciqmc_calc + fciqmc_calc
          ! NOTE: sparse_hamil is currently disabled.
          call do_simple_fciqmc(sys, qmc_in, restart_in, reference, .false.)
  
          nresult = 0
  
  
negative.code: 
          use, intrinsic :: iso_c_binding, only: c_ptr, c_int, c_f_pointer
          use flu_binding, only: flu_State, flu_copyptr
          use aot_table_module, only: aot_table_top, aot_table_close, aot_get_val
  
          use simple_fciqmc, only: do_simple_fciqmc
          use lua_hande_system, only: get_sys_t
  