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v2009.01.01 - Convex Optimization

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5.4. EDM DEFINITION 357<br />

D ∈ EDM N<br />

⇔<br />

{<br />

−V<br />

T<br />

N DV N ∈ S N−1<br />

+<br />

D ∈ S N h<br />

(817)<br />

We provide a rigorous complete more geometric proof of this Schoenberg<br />

criterion in5.9.1.0.4.<br />

[ ] 0 0<br />

T<br />

By substituting G =<br />

0 −VN TDV (815) into D(G) (810), assuming<br />

N<br />

x 1 = 0<br />

[<br />

0<br />

D =<br />

δ ( −VN TDV )<br />

N<br />

] [<br />

1 T + 1 0 δ ( ) ]<br />

−VNDV T T<br />

N<br />

We provide details of this bijection in5.6.2.<br />

[ ] 0 0<br />

T<br />

− 2<br />

0 −VN TDV N<br />

(818)<br />

5.4.2.2 0 geometric center<br />

Assume the geometric center (5.5.1.0.1) of an unknown list X is the origin;<br />

X1 = 0 ⇔ G1 = 0 (819)<br />

Now consider the calculation (I − 1 N 11T )D(G)(I − 1 N 11T ) , a geometric<br />

centering or projection operation. (E.7.2.0.2) Setting D(G) = D for<br />

convenience as in5.4.2.1,<br />

G = − ( D − 1 N (D11T + 11 T D) + 1<br />

N 2 11 T D11 T) 1<br />

2 , X1 = 0<br />

= −V DV 1 2<br />

V GV = −V DV 1 2<br />

∀X<br />

(820)<br />

where more properties of the auxiliary (geometric centering, projection)<br />

matrix<br />

V ∆ = I − 1 N 11T ∈ S N (821)<br />

are found inB.4. V GV may be regarded as a covariance matrix of means 0.<br />

From (820) and the assumption D ∈ S N h we get sufficiency of the more popular<br />

form of Schoenberg’s criterion:

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