Is it possible to implement a LSTM layer after a CNN layer?

I'm trying to implement a CNN layer + a LSTM layer, but I have an error: "Network: Incompatible layer types". Is it not possible to implement this combination in MATLAB or am I just writing it not properly?

My code:

layers = [ ...
    sequenceInputLayer(inputSize)    

      convolution2dLayer(3,8,'Padding','same')
      batchNormalizationLayer
      reluLayer 

      maxPooling2dLayer(2,'Stride',2)

      lstmLayer(numHiddenUnits,'OutputMode','last')

      fullyConnectedLayer(numClasses)
      softmaxLayer
      classificationLayer
      ];

Error:

Error using trainNetwork (line 154)
Invalid network.

Caused by:
    Network: Incompatible layer types. The network contains layer types not supported with recurrent layers.
    Detected recurrent layers:
        layer 6 (LSTM)
    Detected incompatible layers:
        layer 2 (Convolution)
        layer 3 (Batch Normalization)
        layer 5 (Max Pooling)
    Layer 2: Input size mismatch. Size of input to this layer is different from the expected input size.
    Inputs to this layer:
        from layer 1 (output size 500)

[Jake]

I would like to do this as well.

Answer 1

[Mona]

As far as I know, no, you can't combine the two. You can train a CNN independently on your training data, then use the learned features as an input to your LSTM. However, learning and updating CNN weights while training an LSTM is unfortunately not possible.

[krishna Chauhan]

Maam can i store the weights after say a number of epochs of CNN and then use those weights as input to LSTM?

Answer 2

[charu]

use bilstmLayer layer instead of lstm layer as in example

 inputSize = 12;
numHiddenUnits = 100;
numClasses = 9;
layers = [ ...
      sequenceInputLayer(inputSize)
      bilstmLayer(numHiddenUnits,'OutputMode','last')
      fullyConnectedLayer(numClasses)
      softmaxLayer
      classificationLayer]

[Guillaume JUBIEN]

I have the same problem by using a bilstm Layer. The error message is :

if true
Error using trainNetwork (line 154)
Invalid network.
Error in test_spa_REG (line 168)
net = trainNetwork(XTR,TTR,Layers,options);
Caused by:
  Network: Incompatible layer types. The network contains layer types not supported with recurrent layers.
  Detected recurrent layers:
      layer 9 (BiLSTM)
  Detected incompatible layers:
      layer 1 (Image Input)
      layer 2 (Transposed Convolution)
      layer 'temp1' (Convolution)
      layer 5 (Average Pooling)
      and 1 other layers.
  Layer 10: Input size mismatch. Size of input to this layer is different from the expected input size.
  Inputs to this layer:
      from layer 9 (output size 20)

Is it possible to combine CNN with LSTM layer ?

Answer 3

[Shounak Mitra]

Hello Everyone,

As of 19a, MATLAB supports workflows containing both CNN and LSTM layers.

Please check the link that contains an example showing the CNN+LSTM workflow --> https://www.mathworks.com/help/deeplearning/examples/classify-videos-using-deep-learning.html

[Bhavna Rajasekaran]

Is it possible to implement LSTM regression on an image (N-by-M array) such that the output is also a 2-dimesional array? Which means that the Predictors are an N-by-M array of sequences?

[suraj sahoo]

Is the CNN+lstm layer trainable?

Answer 4

[sotiraw sotiroglou]

Matlab 2019a is out. And it claims it can do this cnn - rnn combination.

Could someone give us an example?

Answer 5

[sotiraw sotiroglou]

Matlab 2019a is out there , and it claims it can do this rnn cnn combination.

I dont know the details, but i write this answer to encourage everyone with the same issue to search and maybe help with an example