[SCIP] Farkas pricing

[Gerald Gamrath]

Dear Lan,

you are right, SCIPcolGetRedcost should not be called in that case. The 
assertion alone does not help too much for pinning down the reason for 
the issue, could you run your code with gdb and send me the complete 
backtrace?

Best,
Gerald

Am 07.11.19 um 02:14 schrieb Ngô Lan:
>
> Hi Gerald,
>
>
> Thank you for your fast reply. In my implementation, I do not 
> implement the Farkas pricing but a heuristic in the farkas callback to 
> generate more columns. So I didn't call SCIPcolGetRedcost directly but 
> it was called when the master is resolved after the new column is 
> added. The error I got is "lp.c:3899: SCIPcolGetRedcost: Assertion 
> `lp->validsollp == stat->lpcount' failed."
>
> I was wondering why this error occurred since the master is infeasible 
> so when it is solved again after farkas, it should not call 
> SCIPcolGetRedcost. Or did I do something wrong that leads to that 
> SCIPcolGetRedcost call?
>
>
> Best,
>
> Lan
>
> ------------------------------------------------------------------------
> *From:* Scip <scip-bounces at zib.de> on behalf of Gerald Gamrath 
> <gamrath at zib.de>
> *Sent:* 06 November 2019 12:02:40
> *To:* scip at zib.de
> *Subject:* Re: [SCIP] Farkas pricing
> Dear Lan,
>
> sorry, the documentation is a bit misleading in this case. Similar to 
> constraints, there is a separate method to get the Farkas coefficient 
> for variables. Please use SCIPgetVarFarkasCoef() for this.
>
> Best,
> Gerald
>
> On 06.11.19 02:10, Ngô Lan wrote:
>>
>> Hi all,
>>
>>
>> I am implementing BPC and after some branchings, my master will 
>> become infeasible due to not having enough columns in the pool. 
>> Instead of Farkas pricing, I implement a heuristic to add more 
>> columns into the problem inside the SCIP_DECL_PRICERFARKAS callback. 
>> However I ran into the assertion error "lp->validsollp == 
>> stat->lpcount" in function SCIPcolGetRedcost. I can understand that 
>> this is due to the lastest solution being infeasible but then how 
>> Farkas works normally? It would be great if someone can give me 
>> insight into this. Thank you for your time.
>>
>>
>> Best,
>>
>> Lan
>>
>>
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>

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