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Re: [Help-glpk] lp/mip preprocessor api

From: Heinrich Schuchardt
Subject: Re: [Help-glpk] lp/mip preprocessor api
Date: Sat, 2 Dec 2017 17:58:35 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 12/02/2017 05:54 PM, Andrew Makhorin wrote:
> Hi Heinrich,
>> the API should allow the user to add his own simplifications.
>> This may require access to the npp internal structure.
> It would be problematic. I only plan to include a set of preprocessing
> operations sufficient in most cases (at least for LP). On the other
> hand, if the user needs to perform his own preprocessing, why not to do
> that independently on the glpk preprocessor?

You have already implemented a lot of useful presolving and scaling

If I wanted to build on it and simply add another one I would not like
to reimplement your work.

>> It would be great if the variable mapping could be applied forward and
>> reverse in the MIP callback hook.
> Could you provide an example of what you mean?

In the MIP callback currently we can only access the scaled and
presolved model.

If we could apply the backwards transformation we would be able to
understand the solution in our original variables.

If we could apply the forward transformation we would be able to create
a constraint in our own variables and than add the transformed
constraint to the scaled and presolved model.

Best regards


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