FlaxDiff: A Pedagogical Open-Source Library for Reunderstanding Diffusion Models with Flax and Jax

FlaxDiff is a pedagogical open-source library developed by AshishKumar4, with the core goal of enhancing the readability and comprehensibility of diffusion models, helping developers deeply grasp the mathematical principles behind generative AI. The library provides complete tutorial notebooks from DDPM to EDM, supports multi-host distributed training, and uses the Flax/Jax framework to present clear code in a functional programming style. This thread will introduce its background, core components, tutorial resources, and technology selection across different floors.

Diffusion models have revolutionized the field of generative AI, but the complex mathematical derivations and code implementation have high barriers to entry. FlaxDiff was born out of the author's learning needs: after transitioning from a machine learning researcher to systems engineering, AshishKumar4 wanted to re-master generative AI through a side project. The project was initially developed with Keras/TensorFlow, then migrated to Flax/Jax (due to clearer functional programming), and received support from Google TPU Research Cloud, enabling large model training in distributed environments.

FlaxDiff covers the full-process toolchain of diffusion models:

• Noise Schedulers: LinearNoiseSchedule (basic experiments), CosineNoiseScheduler (stable image generation), CosineContinuousNoiseScheduler, KarrasVENoiseScheduler (inference optimization), EDMNoiseScheduler (best paired with Karras)
• Predictors: EpsilonPredictor (DDPM standard), X0Predictor (directly predicts clean data), VPredictor (commonly used in EDM), KarrasEDMPredictor (general-purpose for EDM)
• Samplers: DDPMSampler (standard process), DDIMSampler (accelerated sampling)

The tutorial notebooks of FlaxDiff are one of its core values; they are written from scratch and do not depend on the library itself:

• Basic Diffusion Model Tutorial: Explains the mathematical principles of DDPM, DDIM acceleration mechanism, and generalized SDE/ODE representations, with Colab links for direct execution
• EDM Tutorial: Dives into EDM's innovative technologies (sampling strategies, network architecture, training techniques) The tutorials are designed to balance accuracy and comprehensibility, making them friendly to beginners.

FlaxDiff uses Flax/Jax instead of PyTorch or TensorFlow/Keras, mainly because Jax's functional programming paradigm, automatic differentiation, and XLA compilation support allow complex diffusion algorithms to be expressed in a concise and composable way. This style is more friendly for teaching and helps understand the essence of the algorithms.

To meet the needs of large-scale model training, FlaxDiff provides Jax-based multi-host data parallel training scripts, demonstrating cross-GPU/TPU training methods. Additionally, the project includes a TPU toolset that simplifies operations such as TPU virtual machine creation, configuration, and dataset mounting.

FlaxDiff does not pursue SOTA performance; instead, it focuses on making diffusion models understandable and learnable. It is suitable for the following groups: students/researchers who want to deeply understand the mathematical principles of diffusion models, developers who want to implement diffusion models from scratch, learners in the Jax/Flax ecosystem, and AI educators. Although the project may have imperfections, the authenticity of "being in the process of learning" makes it more approachable to learners, and it is a good starting point for re-understanding diffusion models.