[SCIP] lp error when adding locally constraint

Tue May 5 08:55:36 CEST 2020

Hi Ambros,

I see. Achterberg's thesis does helps me know deeper about scip.

My current task is to introduce some locally valid cuts to split a search space.
For instance, I need to split the root node into multiple nodes where the union of them is the original search space. And I need to solve the whole subtree rooted at a node once  at a time in a certain order.
It likes doing local branching. I read the implementation of local branching in the given examples, which is done by copy the problem to subscip and solve it.
However in my case, it adds too much additional cost since I need to solve lots of such subscip.
I am currently implementing my own node selector for doing this but it is complicated.
Is there a feasible approch for doing local branching within the scip?

Thanks,
yunzhuang

________________________________
From: Ambros Gleixner <gleixner at zib.de>
Sent: Wednesday, April 29, 2020 1:01 AM
To: Yunzhuang Shen <s3640365 at student.rmit.edu.au>; scip at zib.de <scip at zib.de>
Subject: Re: [SCIP] lp error when adding locally constraint

Hi Yunzhuang,

Am 23.04.20 um 16:36 schrieb Yunzhuang Shen:
> Hi Ambros,
>
> Thanks for your quick response.
>
> After I compiled SCIP and SOPLEX to under debug mode, I cannot reproduce
> the error because the problem did not pass an assertion in the SCIP. The
> backtrace is the following: >
> CO: /home/joey/Downloads/scip-6.0.1/src/scip/tree.c:2403:
> SCIPnodeSetEstimate: Assertion `SCIPsetIsRelGE(set, newestimate,
> node->lowerbound)' failed.
> ==15345==
> ==15345== Process terminating with default action of signal 6 (SIGABRT)
> ==15345==    at 0x69BAE97: raise (raise.c:51)
> ==15345==    by 0x69BC800: abort (abort.c:79)
> ==15345==    by 0x69AC399: __assert_fail_base (assert.c:92)
> ==15345==    by 0x69AC411: __assert_fail (assert.c:101)
> ==15345==    by 0x587623D: SCIPnodeSetEstimate (tree.c:2403)
> ==15345==    by 0x5870E9C: SCIPnodeCreateChild (tree.c:1016)
> ==15345==    by 0x1984F9:
> COML::Branching::split_space_ml_symetric(Scip*, bool)
> (branching_policy.cpp:499)
> ==15345==    by 0x19665B: COML::Branching::scip_execlp(Scip*,
> SCIP_Branchrule*, unsigned int, SCIP_Result*) (branching_policy.cpp:233)
> ==15345==    by 0x199E5F: branchExeclpDynamicBranching
> (branching_policy.cpp:804)
> ==15345==    by 0x54FE318: SCIPbranchruleExecLPSol (branch.c:1589)
> ==15345==    by 0x5500D06: SCIPbranchExecLP (branch.c:2538)
> ==15345==    by 0x578FD2C: SCIPbranchLP (scip_branch.c:1183)
>
> I think I did not pass the correct estimate value when I create the
> child node.

Good.  The assert tells you that the estimate you give should be at
least as large as the lower bound of the current node, on which you
created the branching.  You can query the lower bound with
SCIPnodeGetLowerbound.

> One other thing I need to ask is that the meaning of several
> boolean parameters when create a local constraint. Specifically, do I
> need to change them to other values when I create locally valid
> constraint? (my observation from binpack and tsp example is that some of
> the boolean paramters are different comparing to creating the global
> constraint). My application senario is as the following: right after the
> root node is solved, I create two chlid nodes splited by local
> constraints.

The local flag of SCIPcreateCons (or more specialized ones like
SCIPcreateConsLinear) must be changed.  The other flags are independent,
the usual values should be fine.

> Then I want to put an order on solving those two nodes.

This could mean many things.  Maybe the parameter
"nodeselection/childsel" helps you, see also Chapter 6 of Tobias
Achterberg's thesis

https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fnbn-resolving.de%2Furn%3Anbn%3Ade%3A0297-zib-11129&data=02%7C01%7C%7Ce6bf1ce4b93a42a0553f08d7eb852096%7Cd1323671cdbe4417b4d4bdb24b51316b%7C0%7C0%7C637236829377421172&sdata=Gfy88YOosDIvTxCBvQMGJWCkkyG6UM668YZqV33Sw0o%3D&reserved=0

If you want to fully force your own node processing order in SCIP, then
it might be necessary to implement your own node selector, see

https://aus01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fscip.zib.de%2Fdoc-7.0.0%2Fhtml%2FNODESEL.php&data=02%7C01%7C%7Ce6bf1ce4b93a42a0553f08d7eb852096%7Cd1323671cdbe4417b4d4bdb24b51316b%7C0%7C0%7C637236829377421172&sdata=PZNO4XzG%2BClVerOD127N2ExoIGbn9L3QY9df%2FZt%2Blus%3D&reserved=0

Best,
Ambros

>
> Thank you,
> yunzhuang
> ------------------------------------------------------------------------
> *From:* Scip <scip-bounces at zib.de> on behalf of Ambros Gleixner
> <gleixner at zib.de>
> *Sent:* Thursday, April 23, 2020 11:30 PM
> *To:* scip at zib.de <scip at zib.de>
> *Subject:* Re: [SCIP] lp error when adding locally constraint
> Dear Yunzhuang,
>
> We would need more details in order to help you with this issue.
> Ideally, you
>
> - compile both SoPlex and SCIP in debug mode and provide us with a
> backtrace, and
>
> - run your code through valgrind to check whether there is any memory
> corruption.
>
> I assume you are developing under linux.  It is much easier for us to
> support debugging on linux than on other operating systems.
>
> Best,
> Ambros
>
>
>
>
> Am 23.04.20 um 10:51 schrieb Yunzhuang Shen:
>> Hi there,
>>
>> I am using scip-6.0.1 for my research work. After creating local
>> constraints by setting paramter <local> to true and adding them to
>> nodes, the SCIP terminates after processing a number of nodes. The error
>> is "corrupted size vs. prev_size" and is in inside the soplex solver. My
>> workaround is setting the parameter initial to false so that the
>> constraint is not added to lp. It works but I don't know whether that
>> local constraint is still effective (prune all nodes that is invalid
>> under this local constraint by propagation or other checks). I need to
>> make sure the local contraint is fully effective over the tree whose
>> root is added that local constraint.
>>
>> Thanks,
>> yunzhuang
>>
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>
> --
> Ambros Gleixner, Research Group Mathematical Optimization Methods at
> Zuse Institute Berlin,
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--
Ambros Gleixner, Research Group Mathematical Optimization Methods at
Zuse Institute Berlin, https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.zib.de%2Fgleixner&data=02%7C01%7C%7Ce6bf1ce4b93a42a0553f08d7eb852096%7Cd1323671cdbe4417b4d4bdb24b51316b%7C0%7C0%7C637236829377431168&sdata=Ukf37Mpd6sm7cjNJdDFbRdtm%2FordHsfYmvn381e1tJk%3D&reserved=0

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