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🎓 Research ScientistID: rs-diffusion-score-sde-derivation

Diffusion SDE Stochastic Calculus Proof

扩散模型 SDE 连续随机微分推导
🎯Core Definition
Score-Based Continuous Stochastic Differential Equations (Score SDE, pioneered by Yang Song) unifies discrete DDPMs and score-matching generative models into a continuous-time stochastic calculus framework; the forward noising process is parameterized as an Itô SDE: dx=f(x,t)dt+g(t)dw\mathrm{d}x = f(x, t)\mathrm{d}t + g(t)\mathrm{d}w (ff drift coefficient, gg diffusion coefficient, ww standard Brownian motion); via Anderson's Reverse-Time Theorem, the exact continuous reverse-time generative process is proven to be another closed-form SDE: dx=[f(x,t)g(t)2xlnpt(x)]dt+g(t)dwˉ\mathrm{d}x = [ f(x, t) - g(t)^2 \nabla_x \ln p_t(x) ] \mathrm{d}t + g(t) \mathrm{d}\bar{w}; neural generation simplifies to learning the score function xlnpt(x)\nabla_x \ln p_t(x) via score matching (sθ(x,t)s_\theta(x, t)); furthermore, the deterministic Probability Flow ODE allows standard Runge-Kutta numerical solvers to generate samples in 10-20 steps.
💡Use Cases
Generative AI research scientist theoretical interviews, fast numerical diffusion solver engineering, and Continuous Normalizing Flows.
Key Problems Solved
Discrete 1000-step Markovian sampling is slow and mathematically fragmented; Score SDE delivers a unified continuous stochastic foundation and fast deterministic ODE trajectories.
🎯5 High-Frequency Exam Points
1
Derive the appearance of the score function xlnpt(x)\nabla_x \ln p_t(x) in reverse-time SDEs via Fokker-Planck and Anderson's theorem?
2
Derive the Probability Flow ODE equation and explain why it shares the exact same marginal probability trajectories as the stochastic SDE?
3
Why does Denoising Score Matching (DSM) bypass intractable marginal score calculations by training on known conditional Gaussian kernels?
4
Derive Classifier-Free Guidance (CFG) as a linear extrapolation between conditional and unconditional score estimates?
5
How does DPM-Solver leverage exponential integrators over the semi-linear Probability Flow ODE to achieve photorealistic sampling in under 10 steps?
🔗Foundational Prerequisite Cards (Click to Review)
Updated 2026-08-14
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