Problems and Computer Projects
PROBLEMS
Problem III.1 (Multiple Step-Sizes) Refer to expression (8.18) and choose the matrix B as B = diag{b(l), b(2),…, b(M)} with b(i) > 0. In this case, the recursion (8.20) is replaced by wi = wi–1 + μB[Rdu – Ruwi–1]. This scheme associates one step-size with each entry of the weight vector Wi. Follow the discussion in Sec. 8.2 and derive a necessary and sufficient condition on μ in order to guarantee convergence of wi to
.
Problem III.2 (Product of infinitely many numbers) Consider a scalar recursion of the form x(i) = a(i)x(i – 1) for i ≥ 0, and assume a(i) = e−1/(i+1)2.
- (a) Verify that 0 < a(i) < 1 for all finite i.
- (b) Let
Show that p(i) converges to
, which is a finite positive number. Hint: The series
converges to π2/6.
Problem III.3 (Optimal Step-Size) Refer to expression (9.16) for the optimal step-size. Verify that it is equivalent to the following:

in terms of the squared Euclidean norm of the gradient vector in the numerator, and the ...
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