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Variational Autoencoders in Haskell


This is the repo for a project I did to learn some Haskell, investigating Variational Autoencoders (VAE). You can read the much more in depth, accompanying blog post here. I first tested it with the classic MNIST digits, and then tried encoding both humans and dogs simultaneously for fun.

It's based on the Haskell hmatrix library, which only supports 1D vectors and 2D matrices, but worked well enough here. In it, I implement a NN type, and then a VAE type that's built from NN types. I also implement the Adam optimizer to do the gradient descent.


The human faces data is the UTKFace dataset and the dogs are from the Columbia University dogs dataset. I did a bunch of preprocessing I'll talk about in another post/repo.

Here are a sample of images from each:


This project was built using Cabal 3. It's beyond the scope of this (i.e., it's a bit of a nightmare) to explain how to configure that, but assuming you have, doing

cabal run

should build and run the file with main, vae.hs.

To briefly explain what's going on inside there...

let train_info = TrainInfo  { batch_size = 32
                            , batches_per_epoch = 100
                            , n_epochs = 100
                            , lr = 0.001
                            , beta_KL_max = 0.00
                            , beta_KL_method = "constant"

    data_info_mnist = DataInfo  { n_input = 784
                                , n_tot_samples = 60000
                                , prefix = "mnist"
                                , data_dir = "mnist_data/"

a TrainInfo and DataInfo record each have to be defined. The TrainInfo record determines train parameters you want to use (see the ones in there). beta_KL_method selects which scheme for beta_KL you'd like to use; the simplest is "constant", in which case it's...constant, but other schemes, like a delayed ramp, or a sigmoidal ramp, can be used. beta_KL_max will determine the maximum beta_KL value that it goes up to (if it's a scheme that varies; if it's constant, that's the constant value).

The DataInfo record has info particular to that dataset. It could be figured out automatically, but it was simpler just to give it the info: the input size (mnist is 784=28x28 flattened), 60k total samples, will use the prefix to name output fies, and the data is stored in data_dir.

vae <- build_vae [(n_input data_info), n_hidden, n_latent]

This uses the build_vae to build a VAE type with number of layers based on the numbers you give it. The first number should be the input size, then as many numbers as hidden layers you want. The last number should be the size of the latent dimension that you want. In this case, it only has a single hidden layer (in each of the encoder and decoder). Note that building the VAE automatically builds two NNs inside of it; the encoder NN will have layer sizes [n_input, n_hidden, 2*n_latent] and the decoder will have layer sizes [n_latent, n_hidden, n_input].

let vae_adam_optim = get_init_adam_optim vae (lr train_info)

Similarly, this uses the sizes of the vae just built to built the Adam optimizer.

(new_vae, new_vae_optim, new_train_stats) <- train_n_epochs vae vae_adam_optim train_info data_info

Lastly, you pass the VAE, its optimizer, the TrainInfo record, and the DataInfo record to train_n_epochs, which will repeatedly run through the data, import it, read it, do forward passes, do backward passes, and optimize the weights with gradient descent.


It works very well with MNIST, using a hidden layer of 1,000 and a latent space of 2. For explanations of these, please see the blog post!

No KL div loss:

0.0001 beta_KL, delayed ramp: