[Scip] soplex unable to parse LP file generated by zimpl

[George Nychis]

Note that instead of changing FR[R], I can just force the frequencies of
radios 4 and 5 to 2437 with:

  subto forceBetterSol:
    af[5,2437]==1;

By doing that, I again get the better solution.  But, by leaving it up to
choice it still solves with a lower objective value.  I've been trying to
go through the tutorial to see if I can toy with the different heuristics
to have it find this solution.


On Fri, Jul 26, 2013 at 10:17 AM, George Nychis <gnychis at gmail.com> wrote:

> Hi Gerald and Stefan,
>
> Thanks a bunch for the quick response!  You are correct, it is not a true
> LP. The reason I tried to run it through a different solver is that scip is
> not finding the optimal solution, one that I don't think is "hard" to
> intellectual find, but may for some reason be hard to solve for?  It has
> solved 10/10 tests I created for it (some of which are harder), but 1 of
> these tests it does not find the optimal solution.
>
> In my optimization, I am trying to find the optimal wireless frequency for
> each network.  I give it the possible set of frequencies for each radio:
>   set FR[R]  :=
>     <1> { 2412 },
>     <2> { 2412 },
>     <3> { 2437 },
>     <4> { 2437 },
>     <5> { 2412, 2437 },
>     <6> { 2412, 2437 };
>
> By putting {2412,2437} for <5> and <6>, I allow for the optimization to
> choose between those two frequencies for those two radios (that belong to
> the same network -- they must end up on the same frequency).  When solving
> through scip, it will choose 2412 for these radios which produces an
> objective value of 2.40163428660051.
>
> If I force the two radios to 2437 by removing 2412 from both's set (such
> that there is no choice in the optimization problem), then the objective
> value of 2.73735205292492 will be produced because the radios receive less
> interference on 2437.
>
> Intellectually, this is not hard for me to solve in my head.  Of course,
> with 387 and 794 constraints, I know that what goes on in my head is not
> what happens in the optimization.  But, the only "choices" in the
> optimization are these frequencies and there are only 2.  So, I'm not sure
> why it misses the optimal solution.
>
> Does anyone have any suggestions when running through scip to try and find
> the optimal solution?
>
> I have included the ZIMPL file with a matching data.zpl that forces the
> optimal solution.  You can change FR[R] in data.zpl to match what I pasted
> in this e-mail and if you run it through scip it will find the non-optimal
> solution.  Thanks for any help. This is my first attempt at mixed integer
> programming, so this is all extremely new to me, and I appreciate all the
> work you've all done the optimization suite.
>
> - George
>
>
>
>
> On Fri, Jul 26, 2013 at 4:34 AM, Stefan Vigerske <stefan at math.hu-berlin.de
> > wrote:
>
>> Hi,
>>
>> your model is not an LP, but a quadratic program. SCIP can handle this,
>> but SoPlex cannot.
>>
>> Stefan
>>
>>
>> On 07/26/2013 10:13 AM, George Nychis wrote:
>>
>>> I am trying to run an LP file through soplex that was generated by zimpl.
>>>   However, when I try to I get:
>>>
>>> Loading LP file spectrum_optimization.lp
>>> ELPFRD15 Syntax error in line 205
>>> error while reading file "spectrum_optimization.lp"
>>>
>>> This points to the following lines:
>>>
>>>   airtime_eq_re at 19:
>>>    - RadioAirtime#1 + GoodAirtime#1
>>>    + [ + RadioAirtime#1 * RadioLossRate#1 ]  <--- line 205
>>>   = 0
>>>
>>> I've attached the zmpl files and the lp output.  I am able to run this
>>> through scip using both of these commands:
>>> scip -f spectrum_optimization.zpl
>>> scip -f spectrum_optimization.lp
>>>
>>> So, something seems to be wrong when parsing with soplex.   I'd greatly
>>> appreciate any help.
>>>
>>> Thanks!
>>> George
>>>
>>>
>>>
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>>
>
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