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Re: [Help-glpk] Re: How to create the copy of a node ?

From: Andrew Makhorin
Subject: Re: [Help-glpk] Re: How to create the copy of a node ?
Date: Fri, 13 Feb 2009 07:19:02 +0300

> So basically, I am looking for a chunk of code that I can execute
> within my branching variable selection subroutine that will temporarily
> expand a node, solve the LP relaxation and output the resulting II,
> then get rid of the fact that that node was ever expanded (to keep the
> original tree's integrity), and repeat for the second algorithm choice.

> I originally was just trying to clone the current node, create its
> child, solve the lp relaxation, and then delete the node, but that
> didn't seem to be working for me either. So my professor suggested I
> try copying the entire LP, solve the next node LP relaxation and then
> delete the copy of the LP. Either way, as long I can get my  II_sum for
> the two choices, and then revert to the original parent node and carry
> on without GLPK crashing, I will be very happy.

Probably I misunderstood you. What does "expand a node" means?

If you only need to change the current subproblem (say, to fix some
variables or change their bounds) and then reoptimize its lp relaxation,
you can copy it, make necessary changes, solve it with glp_simplex
as usual, obtain necessary information, and then delete the copy. In any
case I suggest to use glpk api rather than to change the glpk code.

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