[SCIP] Adding Rows using Constraint Handler in SCIP

Fri Jul 3 19:28:58 CEST 2020

Thanks a lot Marc!

These are simple subtour elimination constraints. So I was hoping that once a subtour is discovered, it would be eliminated completely.

________________________________________
From: Scip <scip-bounces at zib.de> on behalf of Marc Pfetsch <pfetsch at mathematik.tu-darmstadt.de>
Sent: Friday, July 3, 2020 5:12 PM
To: scip at zib.de
Subject: Re: [SCIP] Adding Rows using Constraint Handler in SCIP

Dear Naga,

adding rows does not mean that they are added to the LP. In between
there is a filtering process, which might remove some rows depending on
their violation and norm of the normal vector. Without seeing the
details, I think that this seems to be a numerical issue: The constraint
handler adds the row, because it thinks the row is violated, but with
respect to the filtering, the row is not violated. Note that this
depends on the current LP solution. You can force a row to be added to
the LP, but I would suspect that your problem will not go away, because
of the above difference.

Best

Marc

On 03/07/2020 14:12, Naga Venkata Chaitanya Gudapati -
nagavenkata.gudapati at studio.unibo.it wrote:
> Hello,
>
> I had implemented a simple branch-and-cut solver in SCIP to solve a min-max vehicle routing problem by using the TSP example in SCIP as a starting point.
>
> I am able to add rows using the SCIPcreateEmptyRowConshdlr and SCIPaddRow methods as described in the example. It is adding the correct rows but from what I can observe,  the constraint handler is adding the same rows again and again at various points.
>
> For example I add this row: -1e+20 <= +1<t_y_1,2> +1<t_y_2,1> <= 1.999 more than 30 times. My understanding is that once I add a row, the subsequent solutions should violate this  added row. Could someone let me know if I am missing something?
>
>
> Regards,
> Naga
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> https://listserv.zib.de/mailman/listinfo/scip
>
_______________________________________________
Scip mailing list
Scip at zib.de
https://listserv.zib.de/mailman/listinfo/scip