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Author: torontoai

[D] CycleGAN implementation just learning identity mapping

[D] CycleGAN implementation just learning identity mapping

Hi, don’t know where else to ask but I just don’t know what else I could try out with my code.

I’m trying to reimplement CycleGAN in a Jupyter notbook and (for me) the code looks good, but somehow my generators just learn to map an input to itself (so what I put into it comes out at the other end). I’m testing my implementation with the horse2zebra dataset.

First and third row: input, second and fourth row: output

Learning curves for one generator and one discriminator

What’s odd is that the GAN loss is going up, which is probably why the generators don’t learn anything meaningful other than the identity mapping. I also got the feeling that my discriminators just learn to distinguish fake from real images, but nothing about horses or zebras.

Here’s a link to the notebook: https://github.com/kiwiwa/GANs-from-scratch/blob/master/cyclegan/cyclegan.ipynb

I would be so happy if somebody could give me a hint. The discriminator/generator architectures should be fine, probably the training process?

submitted by /u/nottodaymrdick
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[D] What is the consensus on the noise input for GANs?

Is it standard to save the noise distribution your model trained on to use and use the same values for transfer learning / fine tuning / inference?

Or do people typically create a new distribution of noise for the model to learn at each new application?

I’m assuming that during one entire training session you create the noise distribution once so that the model is learning the function of turning that noise into features of the images right?

Thanks in advance!

submitted by /u/Statistical_Incline
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[D] How much of an effect, if any, does batch size have when doing hyperparameter optimization?

I have been using sci-kit optimize to do hyperparameter search (using gp_minimize specifically) for a neural network. I am working on a binary classification problem with a significant class imbalance. I have been using a batch size of 10, but just came across a tweet and notebook by Francois Chollet where he recommended using a high batch size in class imbalance problems in order so that each batch contains at least a few positive examples.

My question is can I just take the networks with the best network architectures I found via my hyperparameter search where I used a batch size of 32, but just retrain them using the same hyperparameters but using a higher batch size?

Or, would batch size have a significant effect on hyperparameter optimization, and I would be better off just redoing hyperparameter optimization but this time with a larger batch size?

Going off of that, any recommendations for how to select batch size? My data contains between 400,000 – 500,000 samples, and I’m feeding in 7 features to the network.

On a similar not of dealing with class imbalance problems – my sample data is weighted to begin with (I am working with a physics problem and the weights for each sample is the probability that that sample will occur), but I was thinking about increasing the weights of the positive data points to maybe help minimize the effect of class imbalance. Thoughts on this?

I hope my question(s) makes sense, thanks for any help!

submitted by /u/Gkg14
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