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Re: [Help-glpk] [Fwd: glp_intopt conversion of solutions via callback]

From: Chris Matrakidis
Subject: Re: [Help-glpk] [Fwd: glp_intopt conversion of solutions via callback]
Date: Sat, 16 Jan 2016 19:24:55 +0200

On 16 January 2016 at 17:17, Sascha Brügmann <address@hidden> wrote:
Michael Hennebry <hennebry <at>> writes:
> Perhaps it would be a good idea to make the presolving and
> scaling transformation available to the user program.
> It could just be a matter of documentation.
> The information must already be somewhere,
> otherwise glpsol could not invert it.
Yes, thats what I'm talking about!

Unfortunately it's not just a matter of documentation: internally, only the transformations to convert solutions of the preprocessed problem back to the original problem are available.

Presumably, you want to use the solution you have to accelerate the solution process. There is a way to do that, but it involves using an undocumented option, so there may be some side effects. You have to set the mip solution values and status for the original problem, which can be done using a file and glp_read_mip() and then set the undocumented option use_sol before calling glp_intopt(), like in this C example:

glp_read_mip(mip, "solution_file");
parm.use_sol = GLP_ON;
glp_intopt(mip, &parm);

Beware: the solution will not be correct for the preprocessed problem until a new one is found. 

Best Regards,

Chris Matrakidis

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