docs: def _init_scratch(self):
          """Initializes a scratch pad equal in size to the wavefunction."""
          scratch = np.zeros((self._num_shards, self._shard_size),
                             dtype=np.complex64)
          scratch_handle = mem_manager.SharedMemManager.create_array(
              scratch.view(dtype=np.float32))
          self._shared_mem_dict['scratch_handle'] = scratch_handle