[SCIP] reoptimization

[Jakob Witzig]

Hi James,

this sounds strange. Which SCIP version do you use? Could you send me 
the original problem file? Otherwise it is hard to see what goes wrong.

Cheers,
Jakob


Am 15.09.2016 um 16:47 schrieb James Cussens:
> Dear Jakob,
>
>
> On 15 September 2016 at 14:14, Jakob Witzig <witzig at zib.de
> <mailto:witzig at zib.de>> wrote:
>
>     Hi James,
>
>     what do you mean exactly with you suspect you doing it wrong? Do you
>     got wrong results?
>
>     Yes, the parameter mentioned below should exactly do the same as you
>     are doing by hand. Do you observe any differences between using the
>     parameter and separating OPTSOL by hand?
>
>
>
> I do observe a difference. When I set reoptimization/sepabestsol = TRUE
> and just do:
> Do k times:
> ---Solve problem    SCIP_CALL( SCIPsolve(scip) );
> ---Inspect best solution: SCIP_CALL( SCIPprintSol(scip,
> SCIPgetBestSol(scip), NULL, FALSE) );
> ---Inspect best solution another way: SCIP_CALL( SCIPprintSol(scip,
> SCIPgetReoptLastOptSol(scip), NULL, FALSE) );
> ---SCIP_CALL( SCIPfreeTransform(scip) );
>
> With one exception, I just get the same optimal solution on each
> iteration. It is as if the parameter is having no effect.
> The exception is that the first call to SCIP_CALL( SCIPprintSol(scip,
> SCIPgetReoptLastOptSol(scip), NULL, FALSE) );  prints out an infeasible
> solution.
>
> Perhaps I am looking in the wrong place for optimal solutions for k>1 or
> somehow preventing the best solutions from each iteration being separated.
>
> James
>
>
>
>
>     Cheers,
>     Jakob
>
>
>     Am 15.09.2016 um 14:03 schrieb James Cussens:
>
>         Dear SCIPers,
>
>         I am using reoptimization to solve a series of binary IPs, and I
>         suspect
>         I am doing it wrong.
>
>         My problem is analogous, I think, to the k-Constrained Shortest Path
>         Problem mentioned in Section 4.2 of Jakob Witzig's master
>         thesis. For my
>         original IP I want to get the optimal solution, then the 2nd
>         best, then
>         3rd best and so on. The objective function never changes.
>
>         I have set reoptimization/enable to TRUE and then do the following:
>
>         Do k times:
>         ---Solve problem    SCIP_CALL( SCIPsolve(scip) );
>         ---store information sufficient to identify optimal solution OPTSOL
>         ---SCIP_CALL( SCIPfreeTransform(scip) );
>         ---add in constraint ruling out just OPTSOL
>
>         I notice that there is a parameter
>         # separate the optimal solution, i.e., for constrained shortest path
>         # [type: bool, range: {TRUE,FALSE}, default: FALSE]
>         reoptimization/sepabestsol = FALSE
>
>         which, I suspect, can be used to do what I am doing 'by hand'.
>         Is this
>         the case?
>
>         More generally, I would appreciate knowing the correct recipe
>         for doing
>         this sort of thing (when using the SCIP callable library).
>
>         James
>
>         --
>         James Cussens
>         Dept of Computer Science &
>         York Centre for Complex Systems Analysis
>         Room 326, The Hub, Deramore Lane            Tel    +44 (0)1904
>         325371 <tel:%2B44%20%280%291904%20325371>
>         University of York                                        Fax  +44
>         (0)1904 500159
>         York YO10 5GE, UK
>          http://www.cs.york.ac.uk/~jc
>         http://www.york.ac.uk/docs/disclaimer/email.htm
>         <http://www.york.ac.uk/docs/disclaimer/email.htm>
>
>
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>
>
>
>     --
>     Jakob Witzig
>
>     Zuse Institute Berlin (ZIB)
>
>     Division Mathematical Optimization and Scientific Information
>     Research Group Mathematical Optimization Methods
>
>     Takustrasse 7
>     14195 Berlin
>
>     Tel. : +49 (0)30 84185-416 <tel:%2B49%20%280%2930%2084185-416>
>     Fax  : +49 (0)30 84185-269 <tel:%2B49%20%280%2930%2084185-269>
>     email: witzig at zib.de <mailto:witzig at zib.de>
>
>
>
>
> --
> James Cussens
> Dept of Computer Science &
> York Centre for Complex Systems Analysis
> Room 326, The Hub, Deramore Lane            Tel    +44 (0)1904 325371
> University of York                                        Fax  +44
> (0)1904 500159
> York YO10 5GE, UK                               http://www.cs.york.ac.uk/~jc
> http://www.york.ac.uk/docs/disclaimer/email.htm


-- 
Jakob Witzig

Zuse Institute Berlin (ZIB)

Division Mathematical Optimization and Scientific Information
Research Group Mathematical Optimization Methods

Takustrasse 7
14195 Berlin

Tel. : +49 (0)30 84185-416
Fax  : +49 (0)30 84185-269
email: witzig at zib.de