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Dec 27, 2011 at 5:34 comment added Woland Oh, and by extra linear constraints I mean additional constraints of the form $c_i(x) \geq 0$, $d_i(y) \geq 0$, $e_i(x) = 0$, $f_i(y) = 0$, where $c,d,e,f$ are linear. These are in addition to the bilinear constraints $y^T x = 0$.
Dec 27, 2011 at 5:30 comment added Woland Thanks Gilead. Unfortunately I can't just assume that $u_{ij} \geq 0$. There is a way to reformulate this problem so that $u_{ij} \geq 0$, but then the bilinear constraints would become $u_{ij}^T \lambda_i = \alpha_{ij}$ for some $\alpha_{ij} \geq 0$, and this would no longer be a complementarity problem. I'm not sure if that formulation would be easier. Alos, I understand NPC != unsolvable, but I am trying to understand the complexity of the problem these equations encode. So I am looking either for a polytime algorithm or an NPC proof.
Dec 24, 2011 at 16:33 comment added Gilead It looks like this could be reformulated into a (mixed) linear complementarity problem (if $u_{ij}$ can be made to be non-negative). There may exist complexity proofs in the LCP literature.
Dec 24, 2011 at 16:28 comment added Gilead Not sure what you mean about "extra linear constraints". You mean the inequality constraints? Also, just a comment: a system being NP-hard does not preclude one from finding a solution. Those statements are not mutually exclusive. A worst-case complexity bound is just that: a bound. The simplex method is NP-hard, but its average performance is extremely good.
Dec 24, 2011 at 8:04 history edited Woland CC BY-SA 3.0
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Dec 24, 2011 at 7:35 history edited Woland CC BY-SA 3.0
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Dec 24, 2011 at 7:25 history asked Woland CC BY-SA 3.0