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I am currently trying to extend the code suggested in this question: How to get layer weight while training?

By using the code below:

class CustomCallback(keras.callbacks.Callback):        
    def on_train_batch_begin(self, batch, logs=None):
        print(model.layers[2].get_weights())

history = model.fit(train_x, train_y, 
                    epochs=200,
                    validation_data=(test_x, test_y), 
                    verbose=1, 
                    callbacks=[CustomCallback()])

I can get the weight of a specific layer of the neural network while training (at the beginning of each iteration of gradient descent for each batch).

My question is, can I use this information and allow loss function's access to it? I would like to use this information to define a new expression to be optimized as a part of custom loss function to be used.

In other words, I would like to access information obtained by callback during each training step for each batch, and feed this information to a custom loss function to define one of objective function term to be optimized.

For instance, consider the following custom loss:

def Custom_Loss(y_true, y_pred):
    return f(y_true, y_pred)

I would like to modify the above defined loss to be as follows:

def Custom_Loss(y_true, y_pred):
    return f(y_true, y_pred) + g(layer_2_weight, y_pred)

One very noob trick that I came up with (but no idea how to do so) is define a "dummy" variable which is redefined inside the callback and use this for the loss function definition, but I am not sure if this would work or if this is a right approach to follow.

If the above-described task is achievable, would it be possible to get some example code or any post in stackoverflow (I tried to find it, but I could not find any. If there is any, please let me know)?

Applicable Math
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    You should implement this with a custom training loop, then you can manipulate any object as desired. Here is a [tutorial](https://www.tensorflow.org/tutorials/customization/custom_training_walkthrough) – Nicolas Gervais Dec 31 '20 at 14:38
  • @NicolasGervais This was extremely helpful! Thanks for the great support, though I could have provided you a vote if you had answered below... – Applicable Math Jan 01 '21 at 07:19

1 Answers1

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Personally, I would do one of the two things listed below,

  • Use Eager Execution ~ While TensorFlow by default now uses this, you would need to, instead of using a Callback and running model.fit(), run the model itself as a function. You can get better information about eager execution on the official TensorFlow Website
  • Use PyTorch ~ I know this question pertains to TensorFlow, but if using PyTorch is an option for you, then such a model training would become simpler in PyTorch.
DJ001
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