Question

在我的自定义损失函数中，我需要调用一个纯python函数，以传递计算出的TD错误和一些索引。该函数不需要返回任何值或进行区分。这是我要调用的函数：

def update_priorities(self, traces_idxs, td_errors):
    """Updates the priorities of the traces with specified indexes."""
    self.priorities[traces_idxs] = td_errors + eps

我尝试使用tf.py_function来调用包装函数，但是只有在将其嵌入到图形中（即，它具有输入和输出并且使用了输出）时，它才会被调用。因此，我尝试通过某些张量而不对它们执行任何操作，然后调用该函数。这是我的整个自定义损失函数：

def masked_q_loss(data, y_pred):
    """Computes the MSE between the Q-values of the actions that were taken and the cumulative
    discounted rewards obtained after taking those actions. Updates trace priorities.
    """
    action_batch, target_qvals, traces_idxs = data[:,0], data[:,1], data[:,2]
    seq = tf.cast(tf.range(0, tf.shape(action_batch)[0]), tf.int32)
    action_idxs = tf.transpose(tf.stack([seq, tf.cast(action_batch, tf.int32)]))
    qvals = tf.gather_nd(y_pred, action_idxs)

    def update_priorities(_qvals, _target_qvals, _traces_idxs):
        """Computes the TD error and updates memory priorities."""
        td_error = _target_qvals - _qvals
        _traces_idxs = tf.cast(_traces_idxs, tf.int32)
        mem.update_priorities(_traces_idxs, td_error)
        return _qvals

    qvals = tf.py_function(func=update_priorities, inp=[qvals, target_qvals, traces_idxs], Tout=[tf.float32])
    return tf.keras.losses.mse(qvals, target_qvals)

但是由于通话mem.update_priorities(_traces_idxs, td_error)

，我收到以下错误消息

ValueError: An operation has `None` for gradient. Please make sure that all of your ops have a gradient defined (i.e. are differentiable). Common ops without gradient: K.argmax, K.round, K.eval.

我不需要为update_priorities计算梯度，我只想在图形计算中的特定点调用它，而不必理会它。我该怎么办？

Answer 1

在包装函数内部的张量上使用.numpy()可以解决此问题：

def update_priorities(_qvals, _target_qvals, _traces_idxs):
    """Computes the TD error and updates memory priorities."""
    td_error = np.abs((_target_qvals - _qvals).numpy())
    _traces_idxs = (tf.cast(_traces_idxs, tf.int32)).numpy()
    mem.update_priorities(_traces_idxs, td_error)
    return _qvals

如何在tf.keras自定义损失函数中触发python函数？

1 个答案: