title: NotImplementedError: Cannot convert a symbolic Tensor (lstm_2/strided_slice:0) to a numpy array. T
body: <p>tensorflow version 2.3.1
  numpy version 1.20</p>
  <p>below the code</p>
  <pre><code># define model
  model = Sequential()
  model.add(LSTM(50, activation='relu', input_shape=(n_steps, n_features)))
  model.add(Dense(1))
  model.compile(optimizer='adam', loss='mse')
  </code></pre>
  <p>we got</p>
  <blockquote>
  <p>NotImplementedError: Cannot convert a symbolic Tensor
  (lstm_2/strided_slice:0) to a numpy array. This error may indicate
  that you're trying to pass a Tensor to a NumPy call, which is not
  supported</p>
  </blockquote>
  <p>it seems to me a crazy error!</p>