[Scip] Transformed constraints

[Julio Rojas]

Thank you very much for your explanation Michael. I'm not programming
with SCIP, as my rudimentary C knowledge wouldn't let me go very far
and I'm already behind my schedule. I create an lp file and pass it to
the standalone solver. Would you care to explain a little bit more the
logicor constraint? In my problem, I have the following constraint
from which I believe it comes:

-1<= 2*y12 - x1 - x2 <= 0
[logicor] <both_x1x2_a>: logicor(<t_y12>, <t_x1_neg>, <t_x2_neg>)

I guess that logicor stands for "logic or", but my constraint is more
of a "logic and" in the sense that if y12 is in the solution then both
x1 and x2 are also part of the solution. Why an "or"?

On the setppc constraint:
[setppc] <both_x5x6_b_clq_0_0>: +<t_y56> +<t_x6_neg> <= 1;

Is this derived from the same original constraint as the logicor? Why
both? I actually included the setppc constraint in my model when I was
starting to define it, but I dropped it later on its development as I
thought it was redundant. I guess not :)

Again, thanks in advance. I don't know where I would be in my thesis
if not for you guys and SCIP. I was fed up by my CPLEX friends (PhD in
OR) laughing at me for using lpsolve. ;)

-------------------------------------------------
Julio Rojas
jcredberry at gmail.com



On Fri, May 14, 2010 at 2:03 AM,  <michael.winkler at zib.de> wrote:
> Hi Julio,
>
>> [logicor] <both_x1x2_a>: logicor(<t_y12>, <t_x1_neg>, <t_x2_neg>);
>> [setppc] <both_x5x6_b_clq_0_0>: +<t_y56> +<t_x6_neg> <= 1;
>>
>> The second one, I think the presolver took it by decomposing another
>> constraint in two. But the first one, I don't have a clue of what it
>> means.
>
> Yes, the presolver extracted the second constraint out of another. The
> first one is an upgraded special linear constraint.
>
>> Can somebody care to explain what "logicor" and "setppc" mean?
>
> "setppc" and "logicor" constraints are a special type of linear
> constraints containing only binary variables and as coefficients and right
> hand side and/or left hand side only ones.
>
> "setppc" comprises three subtypes,
>
> set partitioning: sum_i^n x_i = 1
>
> set packing: sum_i^n x_i <= 1
>
> set cover: sum_i^n x_i >= 1
>
> "logicor" constraints looks like set cover constraints, but are handled
> differently inside SCIP.
>
>> Is there a way to directly include this kind of constraints using the
>> standalone solver?
>
> Do you mean that if the standalone solver is able to read these kind of
> constraints in the format above? Then now, SCIP is not able to read this
> format (CIP format) directly, but we are working on it and hopefully it
> will be possible to read this format after our next release. But you can
> easily write these kinds of constraints as (normal) linear constraints
> (e.g. in lp format) and SCIP will recognize and upgrade them to their
> special linear contraint types.
> ( If you are programming with SCIP, you can call
> SCIPcreateConsLogicor/SCIPcreateConsSetpart/SCIPcreateConsSetpack/SCIPcreateConsSetcover
> to directly create these special types of constraints. See more at
> http://scip.zib.de/doc/html/index.html )
>
> Hope that helps you a little bit, have fun.
>
> Best regards,
>
> Michael
>
>
>> Dear all, I'm really new to linear optimization in general and binary
>> integer programming in particular. I mostly use very simple models for
>> clustering and bundling problems. In one of them I see that there are
>> some transformed constraints after the presolver passes by:
>>
>> [logicor] <both_x1x2_a>: logicor(<t_y12>, <t_x1_neg>, <t_x2_neg>);
>> [setppc] <both_x5x6_b_clq_0_0>: +<t_y56> +<t_x6_neg> <= 1;
>>
>> The second one, I think the presolver took it by decomposing another
>> constraint in two. But the first one, I don't have a clue of what it
>> means. Can somebody care to explain what "logicor" and "setppc" mean?
>> Is there a way to directly include this kind of constraints using the
>> standalone solver?
>>
>> Thanks in advance for your help. Best regards.
>> -------------------------------------------------
>> Julio Rojas
>> jcredberry at gmail.com
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>
>