docs: def initial_state(self, batch_size, dtype=tf.float32, trainable=False,
                      trainable_initializers=None, trainable_regularizers=None,
                      name=None):
      """Builds the default start state tensor of zeros."""
      return self._core.initial_state(
          batch_size, dtype=dtype, trainable=trainable,
          trainable_initializers=trainable_initializers,
          trainable_regularizers=trainable_regularizers, name=name)