deep vector quantization

Implements training code for VQVAE's, i.e. autoencoders with categorical latent variable bottlenecks, which are then easy to subsequently plug into existing infrastructure for modeling sequences of discrete variables (GPT and friends). dvq/vqvae.py is the entry point of the training script and a small training run can be called e.g. as:

cd dvq; python vqvae.py --gpus 1 --data_dir /somewhere/to/store/cifar10

This will reproduce the original DeepMind VQVAE paper (see references before) using a semi-small network on CIFAR-10. Work on this repo is ongoing and for now requires reading of code and understanding these approaches. Next up aiming to reproduce DALL-E result, for this most of the code is in place but we need to train with the logit laplace distribution, tune the gumbel softmax hyperparameters, and train on ImageNet+.

References

DeepMind's VQVAE

The VQVAE from the paper can be trained with --vq_flavor vqvae --enc_dec_flavor deepmind. I am able to get what I think are expected results on CIFAR-10 using VQVAE (judging by reconstruction loss achieved). However I had to resort to a data-driven intialization scheme with k-means (which is with current implementation not multi-gpu compatible), and which the sonnet repo does not use, potentially due to more careful model initialization treatment. When I do not use data-driven init the training exhibits catastrophic index collapse.

Jang et al. Gumbel Softmax

For this use --vq_flavor gumbel. Trains and converges to slightly higher reconstruction loss, but tuning the scale of the kl divergence loss and the temperature decay rate and the version of gumbel (soft/hard) has so far proved a little bit finicky. Also the whole thing trains much slower. Requires a bit more thorough hyperparameter search than a few one-off guesses.

OpenAI's DALL-E

Re-implementation is not yet complete, e.g. we still use MSE is still used as a loss, we still only train on CIFAR and use a smaller network, etc. However, the different encoder/decoder architecture trains and gives comparable results to the (simpler) DeepMind version on untuned 1-GPU trial runs on stride /4 VQVAEs. Situation is developing...