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Re: How to retrieve intermediate solutions of MIP problems without inter

From: Domingo Alvarez Duarte
Subject: Re: How to retrieve intermediate solutions of MIP problems without interrupting the solver?
Date: Mon, 10 Aug 2020 12:00:04 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

Hello Heinrich !

Thank you for reply !

My bad, I did followed the code instead of reading the manual !

There is a old saying:

When everything else fails, read the  manual !

Cheers !

On 10/8/20 11:56, Heinrich Schuchardt wrote:
On 10.08.20 11:47, Domingo Alvarez Duarte wrote:
Hello Yuri !

Following the code again I found this lines in examples/glpsol.c:


#ifdef GLP_CB_FUNC /* 05/IV-2016 */
          {  extern void GLP_CB_FUNC(glp_tree *, void *);
             csa->iocp.cb_func = GLP_CB_FUNC;
             csa->iocp.cb_info = NULL;


It seems that the user callback can be set that way but could not found
any other reference so far.

The callback is described in chapter 5.1.1 "Using the callback routine"
of doc/glpk.pdf. There is a reason code

GLP_IBINGO — better integer solution found.

Best regards


Cheers !

On 9/8/20 20:04, Yuri wrote:
For my problem Glpk quickly finds some solution and then goes on to
find better solutions and this takes a lot of time.

I'm interested in all solutions, beginning from the first integer
solution in finds.

I couldn't find a callback that is called when a better solution
becomes known.

For example, in this run it called glp_intopt which progressively
found 3 solutions, each better than the previous one:

Long-step dual simplex will be used
+   633: mip =     not found yet >=              -inf (1; 0)
+  1006: >>>>>   1.098691667e+01 >= 5.512339583e+00  49.8% (18; 0)
+  4134: >>>>>   1.098525000e+01 >= 6.681520833e+00  39.2% (31; 22)
+  7210: >>>>>   1.098458333e+01 >= 1.043275926e+01   5.0% (24; 87)
+  7654: mip =   1.098458333e+01 >=     tree is empty   0.0% (0; 195)

I am looking for access to all of  them as they become available.


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