anchor.diff:          !       qmc = { ... },
           !       restart = { ... },
           !       reference = { ... },
  +        !       sparse_hamil = true/false,
           !    }
   
           ! See interface documentation for the relevant read_TYPE procedure to
  
positive.code:         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']
  
          lua_state = flu_copyptr(L)
          call get_sys_t(lua_state, sys)
  
negative.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 aot_get_val(use_sparse_hamil, err, lua_state, opts, 'sparse_hamil', default=.true.)
          call warn_unused_args(lua_state, keys, opts)
          call aot_table_close(lua_state, opts)
  
          calc_type = simple_fciqmc_calc + fciqmc_calc
          call do_simple_fciqmc(sys, qmc_in, restart_in, reference, use_sparse_hamil)
  
          nresult = 0
  
  