Reproducibility And ML Projects

Pete Warden explains some of the difficulties around reproducing ML models:

Why does this all matter? I’ve had several friends contact me about their struggles reproducing published models as baselines for their own papers. If they can’t get the same accuracy that the original authors did, how can they tell if their new approach is an improvement? It’s also clearly concerning to rely on models in production systems if you don’t have a way of rebuilding them to cope with changed requirements or platforms. At that point your model moves from being a high-interest credit card of technical debt to something more like what a loan-shark offers. It’s also stifling for research experimentation; since making changes to code or training data can be hard to roll back it’s a lot more risky to try different variations, just like coding without source control raises the cost of experimenting with changes.

It’s not all doom and gloom, there are some notable efforts around reproducibility happening in the community. One of my favorites is the TensorFlow Benchmarks project Toby Boyd’s leading. He’s made it his team’s mission not only to lay out exactly how to train some of the leading models from scratch with high training speed on a lot of different platforms, but also ensures that the models train to the expected accuracy. I’ve seen him sweat blood trying to get models up to that precision, since variations in any of the steps I listed above can affect the results and there’s no easy way to debug what the underlying cause is, even with help from the authors. It’s also a never-ending job, since changes in TensorFlow, in GPU drivers, or even datasets, can all hurt accuracy in subtle ways. By doing this work, Toby’s team helps us spot and fix bugs caused by changes in TensorFlow in the models they cover, and chase down issues caused by external dependencies, but it’s hard to scale beyond a comparatively small set of platforms and models.

I see two separate problems:  reproducing the process and reproducing the result.  Reproducing the process is why you want to use something like notebooks:  it’s a proof that you (and others!) can generate the same type of model the same way multiple times.  Reproducing the result is harder given the stochastic nature of ML, but if you’re following the same process, you’re at least more likely to end up close to the same result.

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March 2018
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