anchor.diff:          !     nanalyse = N,
           !     blacs_block_size = block_size,
           !     rdm = { ... }, -- L-d vector containing the sites to include in subsystem A.
  -        !     sparse_hamil = true/false
           ! }
           ! lanczos = {
           !     neigv = N,
           !     nbasis = M,
           !     direct = true/false,
  +        !     sparse = true/false, -- default true
           ! }
   
           ! In/Out:
  
positive.code:         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)
  
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', default=.true.)
          call warn_unused_args(lua_state, keys, opts)
          call aot_table_close(lua_state, opts)
  
  