[Clp] Question about ClpPrimalColumnPivot.PivotColumn

[Dami Choi]

Hello,

I'm still very new to the codebase, and I'm also definitely not
knowledgeable in terms of linear programming (I studied the Bertsimas and
tsitsiklis intro to linear optimization and that's it), so I apologize for
my stupid questions. I tried to read the comments and the documentation (
https://www.coin-or.org/Doxygen/Clp/) as much as possible, but I'm still a
bit confused.

First of all, what does dj stand for?
In the djRegion function in ClpSimplex (
https://projects.coin-or.org/Clp/browser/trunk/src/ClpSimplex.hpp#L1146),
what does the section argument mean?

In the PivotColumn function in ClpPrimalColumnPivot, what is the purpose of
the arguments updates and sparerow/columns? If I understand correctly, only
updates contains some information from the previous iteration, and
sparerow/column aids in the computation in the process of updating the
costs. But in what part of the simplex algorithm does this updating cost
correspond to, and why is it in the PivotColumn function and not in the
primal function?

Thank you,

Dami
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