12.07.2015 Views

v2010.10.26 - Convex Optimization

v2010.10.26 - Convex Optimization

v2010.10.26 - Convex Optimization

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

608 APPENDIX A. LINEAR ALGEBRANow let A,B ∈ S M have diagonalizations A=QΛQ T and B=UΥU T withλ(A)=δ(Λ) and λ(B)=δ(Υ) arranged in nonincreasing order. Thenwhere S = QU T . [393,7.5]A ≽ B ⇔ λ(A−B) ≽ 0 (1500)A ≽ B ⇒ λ(A) ≽ λ(B) (1501)A ≽ B λ(A) ≽ λ(B) (1502)S T AS ≽ B ⇐ λ(A) ≽ λ(B) (1503)A.3.1.0.2 Theorem. (Weyl) Eigenvalues of sum. [202,4.3.1]For A,B∈ R M×M , place the eigenvalues of each symmetrized matrix intothe respective vectors λ ( 1(A 2 +AT ) ) , λ ( 1(B 2 +BT ) ) ∈ R M in nonincreasingorder so λ ( 1(A 2 +AT ) ) holds the largest eigenvalue of symmetrized A while1λ ( 1(B 2 +BT ) ) holds the largest eigenvalue of symmetrized B , and so on.1Then, for any k ∈{1... M }λ ( A +A T) k + λ( B +B T) M ≤ λ( (A +A T ) + (B +B T ) ) k ≤ λ( A +A T) k + λ( B +B T) 1⋄(1504)Weyl’s theorem establishes: concavity of the smallest λ M and convexityof the largest eigenvalue λ 1 of a symmetric matrix, via (497), and positivesemidefiniteness of a sum of positive semidefinite matrices; for A,B∈ S M +λ(A) k + λ(B) M ≤ λ(A + B) k ≤ λ(A) k + λ(B) 1 (1505)Because S M + is a convex cone (2.9.0.0.1), then by (175)A,B ≽ 0 ⇒ ζA + ξB ≽ 0 for all ζ,ξ ≥ 0 (1506)A.3.1.0.3 Corollary. Eigenvalues of sum and difference. [202,4.3]For A∈ S M and B ∈ S M + , place the eigenvalues of each matrix into respectivevectors λ(A), λ(B)∈ R M in nonincreasing order so λ(A) 1 holds the largesteigenvalue of A while λ(B) 1 holds the largest eigenvalue of B , and so on.Then, for any k ∈{1... M }λ(A − B) k ≤ λ(A) k ≤ λ(A +B) k (1507)⋄⋄

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!