Automatically Flatten & Unflatten Nested Containers

This post is about a small functionality that is found useful in TensorFlow / JAX / PyTorch.

Low-level components of these systems often use a plain list of values/tensors as inputs & outputs. However, end-users that develop models often want to work with more complicated data structures: Dict[str, Any], List[Any], custom classes, and their nested combinations. Therefore, we need bidirectional conversion between nested structures and a plain list of tensors. I found that different libraries invent similar approaches to solve this problem, and it's interesting to list them here.

Read more

TorchScript: Tracing vs. Scripting

PyTorch provides two methods to turn an nn.Module into a graph represented in TorchScript format: tracing and scripting. This article will:

  1. Compare their pros and cons, with a focus on useful tips for tracing.
  2. Try to convince you that torch.jit.trace should be preferred over torch.jit.script for deployment of non-trivial models.
Read more

Where Are Pixels? -- a Deep Learning Perspective

Technically, an image is a function that maps a continuous domain, e.g. a box , to intensities such as (R, G, B). To store it on computer memory, an image is discretized to an array array[H][W], where each element array[i][j] is a pixel.

How does discretization work? How does a discrete pixel relate to the abstract notion of the underlying continuous image? These basic questions play an important role in computer graphics & computer vision algorithms.

This article discusses these low-level details, and how they affect our CNN models and deep learning libraries. If you ever wonder which resize function to use or whether you should add/subtract 0.5 or 1 to some pixel coordinates, you may find answers here. Interestingly, these details have contributed to many accuracy improvements in Detectron and Detectron2.

Read more

Deep Learning Experiments and Claims

这几年来, 从 FAIR 的几位大佬身边学习到的最多的是对待 research 的态度. 因此说说写 paper 和做实验的体会.

实验与 claims

实验是为了证明或强化文章里给出的 claim/hypothesis 的.

Ross ICCV 2019 tutorial 最后谈了谈怎么写 paper. 第 126 页说, 文章中所有的 claim, 理想情况下都应该要么是文献中已有的 claim, 要么是有实验能够证明的 claim.

Read more

Unawareness of Deep Learning Mistakes

TL;DR: People are hardly aware of any deep learning mistakes they made, because things always appear to work, and there are no expectations on how well they should work. The solution is to try to accurately reproduce settings & performance of high-quality papers & code.

Read more