- Try to test your LSTM network in MATLAB first. Does it match the validation data. If it does, then the issue is with a Simulink model.
- If your validation data in Simulink does not start at time 0, you need to reset the state of LSTM in State and Predict block by putting this block into a resettable subsystem and triggering it before your data starts. Ie. if your data starts at t-0.2, then do a step from 0 to 1 at 0.1 sec and feed that into reset port of resettable susbystem to reset the state.
Deep learning Toolbox - LSTM Training
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Hi All,
I am building an LSTM ROM to integrate into my Simscape model, which is using training and test data captured in ANSYS Chemkin software.
I have had multiple issues with pre-processing the data, which I am working through, that main reason being is ANSYS only uses a variable step solver.
I am basing my code on the LSTM ROM example. The validation of the LSTM model (before we integrate into the full Simscape model) will have to be a simple model using the "Stateful Predict" block, and then using the test and train data captured in the workspace to comapre to the LSTM model, using "From Workspace" array block to get the signals into Simulink.
I have been able to run the code, and the training progress seems that the model has minimised the RMSE and loss, however, when I try to run my simple validaton model the results show something else!, see below.
As I am unsure as to how to proceed with debugging, I am unsure whether it is the pre-processed data (which may need resampling), the LSTM network and parameter selection or the validation model that is the main cause.
My question is, can I now use the Deep Network Designer app to help debugging. Now using the code generated the concatenated data is now in a 10x1 cell, can I now save this as a datastore and use the app to train the network?
I can show the training progress, data structure and validation output below.
Training Progress:
Validation Model:
Validation Results: Test data top row, LSTM data bottom row.
Any suggestions on how to proceed would be great, as stuck as to how to proceed.
Thanks in advance,
Patrick
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Answers (1)
Arkadiy Turevskiy
on 2 Sep 2022
Hi Patrick,
Two suggestions:
Arkadiy
3 Comments
Ben
on 6 Sep 2022
I'll add a few additional notes to Arkadiy's answer here to help debug further. A variation on 1. would be to try run the Simulink model with your training data, since you have an expectation of how that should perform from the training plot.
It may be useful to add additional outputs to the workspace exactly before the input and after the output of the Stateful Predict block. This will help check exactly what data is passed to the LSTM and that the LSTM outputs, and you can compare this to how the network was trained in MATLAB.
A few possible issues come to mind:
- Arkadiy's point 2. on the LSTM state - it will only be reset at time 0, or when the stateful predict block is inside a resettable subsystem and a reset signal is received.
- Simulink is taking different time steps to your data. The Rate Transition block has a NoOp label, but if you are using input data with uniform timesteps, and a variable step solver in Simulink, then I would expect this to be something else such as ZOH. This should be possible by setting the output port sample time of the Rate Transition block to match the uniform timesteps of your input data. Essentially the issue is that Simulink's variable step ODE solvers may take different timesteps to your input data which will corrupt the LSTM state. A potential alternative would be to swap Simulink's ODE solver to a fixed step ODE solver with step size matching your input data, but this may not be realistic when the ROM part of a larger system.
- The validation data is simply too different to the training data and the model can't perform well on it. This will depend on the strategy used to split validation off from the initial dataset. You could check this by including the validation data during training - the plot will then contain the current loss on the validation data, which should roughly follow the training loss if the model is generalising well to the validation data.
Hope that helps,
Ben
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