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Thanks Ambros for your advice.
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<div class="">Marcus.</div>
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<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">________________________________</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Marcus R Garvie</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Associate Professor</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Rm 552 MacNaughton Bldg</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Dept. of Math & Stats</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">University of Guelph</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Guelph, ON Canada N1G 2W1</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Tel. 519-824-4120 ext 53409</font></div>
<div style="font-size: 12px; orphans: 2; widows: 2; margin: 0px;" class=""><font face="Helvetica" class="">Email. <a href="mailto:mgarvie@uoguelph.ca" class=""><font color="#0020e3" style="color: rgb(0, 32, 227);" class=""><u class="">mgarvie@uoguelph.ca</u></font></a></font></div>
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<div class="">On Jun 15, 2018, at 4:37 AM, Ambros Gleixner <<a href="mailto:gleixner@zib.de" class="">gleixner@zib.de</a>> wrote:</div>
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<div class="">Hi Pierre and Marcus,<br class="">
<br class="">
The attached problem was small and also SCIP/SoPlex solves it easily. Marcus sent me a larger instance. These seem pure feasibility problems with a tight dual bound of 0, but hard combinatorial structure.<br class="">
<br class="">
Marcus: Maybe adding an artificial objective function helps to direct the search, certainly turning off separation and maybe also strongbranching should speed things up. But potentially SCIP is missing a heuristic that makes the commercial solvers more successful.<br class="">
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Best,<br class="">
Ambros<br class="">
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Am 15.06.2018 um 02:54 schrieb Pierre Le Bodic:<br class="">
<blockquote type="cite" class="">Hi Marcus,<br class="">
I gave a try to your problem. Using scip 5.0.1 and gurobi 8.0.0 as the LP solver, I get a feasible solution in less than a second. Log attached. Please let me know if you can't replicate this.<br class="">
Kind regards,<br class="">
Pierre<br class="">
On 15 June 2018 at 08:38, Ambros Gleixner <<a href="mailto:gleixner@zib.de" class="">gleixner@zib.de</a> <<a href="mailto:gleixner@zib.de" class="">mailto:gleixner@zib.de</a>>> wrote:<br class="">
Hi Marcus,<br class="">
28456 variables are in general not particularly large, but for hard<br class="">
problems, also medium-sized instances can become very difficult.<br class="">
Gurobi is known to be stronger than SCIP, but it could be that with<br class="">
the right parameters also SCIP can solve the instances. As a<br class="">
starter try to change emphasis settings, one or more of<br class="">
set presolving emphasis aggressive<br class="">
set separating emphasis {off,fast,aggressive}<br class="">
set heuristics emphasis aggressive<br class="">
set emphasis {feasibility,optimality,hardlp}<br class="">
and/or look at the statistics via "display statistics" to find<br class="">
expensive and unsuccessful plugins to be deactivated.<br class="">
But giving more detailed advice here is difficult without seeing the<br class="">
instance. You can send me a larger, problematic instance of your<br class="">
model as a personal message, and I will try to find the time to look<br class="">
at it.<br class="">
Best,<br class="">
Ambros<br class="">
Am 14.06.2018 um 23:21 schrieb Marcus Garvie:<br class="">
Hi everyone,<br class="">
this is my first post, so please understand that my knowledge of<br class="">
SCIP is low!<br class="">
I have been solving some large binary linear programming<br class="">
problems with no objective function. I solve .LP files using a<br class="">
terminal to issue the commands on my Mac. The .LP files are<br class="">
automatically generated, with e.g. the attached format.<br class="">
The only commands I issue are<br class="">
SCIP> read test.lp<br class="">
SCIP> optimize test.lp<br class="">
The problem is that for very large problems (e.g. 28456<br class="">
variables) the solver seems to be running forever (> 2 days)! I<br class="">
tried the same problem in Gurobi and it gave me the correct<br class="">
solution in 15 minutes. (I’m wanting to use SCIP because it has<br class="">
some easy options for giving me all feasible solutions, while<br class="">
Gurobi does not).<br class="">
I also tried the problem in CPLEX, but it has some limitations<br class="">
on the length of the variable names (Error 1464) so I’m a<br class="">
little stuck if I want multiple solutions for large problems.<br class="">
Any advice would be appreciated.<br class="">
Marcus.<br class="">
PS I only know how to problems in the .LP format!<br class="">
________________________________<br class="">
Marcus R Garvie<br class="">
Associate Professor<br class="">
Rm 552 MacNaughton Bldg<br class="">
Dept. of Math & Stats<br class="">
University of Guelph<br class="">
Guelph, ON Canada N1G 2W1<br class="">
Tel. 519-824-4120 ext 53409<br class="">
Email. _<a href="mailto:mgarvie@uoguelph.ca" class="">mgarvie@uoguelph.ca</a>_ <<a href="mailto:mgarvie@uoguelph.ca" class="">mailto:mgarvie@uoguelph.ca</a><br class="">
<<a href="mailto:mgarvie@uoguelph.ca" class="">mailto:mgarvie@uoguelph.ca</a>>><br class="">
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-- Ambros Gleixner, Research Group Mathematical Optimization Methods at<br class="">
Zuse Institute Berlin, <a href="http://www.zib.de/gleixner" class="">http://www.zib.de/gleixner</a><br class="">
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<br class="">
-- <br class="">
Ambros Gleixner, Research Group Mathematical Optimization Methods at Zuse Institute Berlin,
<a href="http://www.zib.de/gleixner" class="">http://www.zib.de/gleixner</a><br class="">
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