v2007.09.13 - Convex Optimization

440 CHAPTER 7. PROXIMITY PROBLEMS......❜..❜..❜..❜..❜..❜..❜.❜❜❜❜❜❜❜✧ ✧✧✧✧✧✧✧✧✧✧✧✧✧✧ 0 ✟✟✟✟✟✟✟✟✟✟✟EDM N❜❜ S N ❝ ❝❝❝❝❝❝❝❝❝❝❝h❜❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❜❜❜❜❜❜ K = S N .h ∩ R N×N+.❜... S N ❜.. ❜..❜.. ❜❜❜ ✧ ✧✧✧✧✧✧✧✧✧✧✧✧✧✧....... . . . ..R N×N........................Figure 108: Pseudo-Venn diagram: The EDM cone belongs to theintersection of the symmetric hollow subspace with the nonnegative orthant;EDM N ⊆ K (704). EDM N cannot exist outside S N h , but R N×N+ does.......7.0.1.2 Egregious input error under nonnegativity demandMore pertinent to the optimization problems presented herein whereC ∆ = EDM N ⊆ K = S N h ∩ R N×N+ (1107)then should some particular realization of a proximity problem demandinput H be nonnegative, and were we only to zero negative entries of anonsymmetric nonhollow input H prior to optimization, then the ensuingprojection on EDM N would be guaranteed incorrect (out of order).Now comes a surprising fact: Even were we to correctly follow theorder-of-projection rule and provide H ∈ K prior to optimization, then theensuing projection on EDM N will be incorrect whenever input H has negativeentries and some proximity problem demands nonnegative input H .