KLDivLoss error on backward pass

Hello everyone,
I’m trying to add a sparsity constraint (as in a sparse autoencoder) to my model using nn.KLDivLoss() on the activation probability of the hidden units

Here’s my code:

criterion1 = nn.MSELoss()
criterion2 = nn.KLDivLoss(size_average=False)
optimizer = torch.optim.Adam(model.parameters(), lr=learning_rate)

for epoch in range(num_epochs):
    for data in dataloader:

        img = Variable(data)

        #forward pass
        output = model(img)
        loss1 = criterion1(output, img)
        loss2 = criterion2(model.p_.log(), p) + criterion2((1-model.p_).log(),1-p)
        loss = loss1 + loss2

        #backward pass

But then I get this error at the 2nd iteration

RuntimeError: Trying to backward through the graph a second time, but the buffers have already been freed. Specify retain_graph=True when calling backward the first time.

if I use just “nn.MSELoss()” as criterion everything works just fine.
Needless to say, if I put “retain_graph=True” the model starts allocating memory at every iteration and my GPU runs out of memory almost immediately.

What is your model and what is model.p_?

Hi Richard,
It’s a variable inside my model where I store the activation probability of the hidden units, my model is basically an autoencoder, so Input and Output have the same size.

This looks like it could be a bug. Could you provide a minimal example (or even just code that I can run) that reproduces this?

I’m back, I think I fixed it simply by adding p_ as an output of my model instead of having it as “model.p_” (defined at initialization and then updated during learning).
Thanks for the help :wink: