Optimization for Machine Learning I
summary
Casts learning as optimization over parameters and proves convex relaxations let local gradient info give global guarantees; uses stochastic gradient descent (one-sample updates) derived from follow-the-regularized-leader and shows expected error/regret scales as 1/sqrt(T), so epsilon accuracy needs O(1/epsilon^2) iterations. Presents FTRL/entropy and Euclidean regularizers (recovering multiplicative weights and GD), explains AdaGrad’s adaptive matrices for sparse data and claims instance-dependent √d improvements in regret.
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chapters (18)
- 0:00Intro
- 3:15Mathematical optimization
- 5:03Learning - optimization over data laka. Empirical Risk Minimization
- 7:02Example: linear classification
- 11:29Convexity
- 14:11Convex relaxations for linear & kernel
- 16:16Gradient descent, constrained set
- 17:50Convergence of gradient descent
- 24:43Gradient Descent -caveat
- 27:17Statistical (PAC) learning
- 32:33Online gradient descent Zinkevich '05
- 34:31More powerful setting: Online Learning in Games
- 37:19Analysis
- 39:18Lower bound
- 45:10Stochastic gradient descent
- 47:38Stochastic vs. full gradient descent
- 53:24Minimize regret: best-in-hindsight
- 56:30Fixing FTL: Follow-The-Regularized-Leader (FTRL)
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