# Yuriy Zinchenko

Gurobi Staff
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## Activity overview

Latest activity by Yuriy Zinchenko
• Yuriy Zinchenko commented,

Official comment

Hello again, Andrey. Thank you again for asking an interesting Q.  The problem instance you have shared is small, but is seemingly tough to determine feasibility.  Our apologies for not replying so...

• Yuriy Zinchenko commented,

Great to hear this is helpful. Stay well, Ramy, and please say "hello" to John if you run into him; he may remember Yuriy who was a PDF at McMaster when Professor Chinneck visited. Regards.

• Yuriy Zinchenko commented,

> If Guroubi computes IIS using a filtering algorithm, that means we can attempt to get multiple IISes by shuffling the constraints in the model, correct? I tried doing that but Guroubi's computIIS...

• Yuriy Zinchenko commented,

Official comment

Hello Ramy, Thanks for asking! :) 1. For LP, computing all III's based on the dual, as you said, is equivalent to enumerating all the vertices of the respective dual polyhedron, which could be a ma...

• Yuriy Zinchenko commented,

Official comment

Hello Taejoon, 1) for a polytope {x: Ax <= b} the analytic centre x* is computed as a minimizer of the log-barrier,  x* = arg min { -\sum_i (b - Ax)_i : Ax <= b } Now, if LP has multiple solutions,...

• Yuriy Zinchenko commented,

Official comment

Hello Bo:   we do apply dual transformation automatically (in some cases), specifically, indeed, when A is "long and narrow" we would look into that with the code. In other words, the matrix "aspec...

• Yuriy Zinchenko commented,

Hello Yannic: barHomogeneous = 1 parameter refers to using the so-called homogeneous self-dual embedding that amongst other things allows to set the initial point for the barrier (the other alterna...

• Yuriy Zinchenko commented,

Hi Geoffroy, could you please elaborate on > I do not find the same values as the latest displayed by the Barrier Logging perhaps with the snapshot of the log, and a brief explanation on how check ...

• Yuriy Zinchenko commented,

Hi Dominique, sorry I have somehow missed your Q:( and thank you Jarek! (yes, we do scale) Wish you stay well in 2021!! (we are fine in Calgary, it is a bit cold now, about -30C, but no complains o...

• Yuriy Zinchenko commented,

Hello Dominique, 1. I believe the residual values are unscaled, and 2. the norm is simply the max (or $$\ell_{\infty}$$) norm. You can find a bit more info here, https://www.gurobi.com/documentatio...