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v2009.01.01 - Convex Optimization

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6.8. DUAL EDM CONE 485<br />

6.8.1.3.1 Exercise. Dual EDM spectral cone.<br />

Find a spectral cone as in5.11.2 corresponding to EDM N∗ .<br />

<br />

6.8.1.4 Nonorthogonal components of dual EDM<br />

Now we tie construct (1174) for the dual EDM cone together with the matrix<br />

criterion (1179) for dual EDM cone membership. For any D ∗ ∈ S N it is<br />

obvious:<br />

δ(D ∗ 1) ∈ S N⊥<br />

h (1184)<br />

any diagonal matrix belongs to the subspace of diagonal matrices (60). We<br />

know when D ∗ ∈ EDM N∗ δ(D ∗ 1) − D ∗ ∈ S N c ∩ S N + (1185)<br />

this adjoint expression (1182) belongs to that face (1146) of the positive<br />

semidefinite cone S N + in the geometric center subspace. Any nonzero<br />

dual EDM<br />

D ∗ = δ(D ∗ 1) − (δ(D ∗ 1) − D ∗ ) ∈ S N⊥<br />

h ⊖ S N c ∩ S N + = EDM N∗ (1186)<br />

can therefore be expressed as the difference of two linearly independent<br />

nonorthogonal components (Figure 105, Figure 126).<br />

6.8.1.5 Affine dimension complementarity<br />

From6.8.1.3 we have, for some A∈ S N−1<br />

+ (confer (1185))<br />

δ(D ∗ 1) − D ∗ = V N AV T N ∈ S N c ∩ S N + (1187)<br />

if and only if D ∗ belongs to the dual EDM cone. Call rank(V N AV T N ) dual<br />

affine dimension. Empirically, we find a complementary relationship in affine<br />

dimension between the projection of some arbitrary symmetric matrix H on<br />

the polar EDM cone, EDM N◦ = −EDM N∗ , and its projection on the EDM<br />

cone; id est, the optimal solution of 6.11<br />

minimize ‖D ◦ − H‖ F<br />

D ◦ ∈ S N<br />

subject to D ◦ − δ(D ◦ 1) ≽ 0<br />

(1188)<br />

6.11 This dual projection can be solved quickly (without semidefinite programming) via

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