Gradient descent on a quadratic

Problem

For f(w)=(w3)2f(w)=(w-3)^2, start at w0=0w_0=0. Compute w1w_1 for learning rates 0.10.1 and 1.11.1. Explain which update moves toward the minimizer and why overly large learning rates can diverge.

Reveal answer or reference solution

The gradient at 00 is 6-6. With η=0.1\eta=0.1, w1=0.6w_1=0.6. With η=1.1\eta=1.1, w1=6.6w_1=6.6, overshooting 33. For this quadratic, convergence requires 0<η<10<\eta<1; larger steps amplify error.

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