How to Resolve ERROR: invalid SCIP stage <10> in SCIP C++

Question

I feel like I am missing something very simple and very straightforward. I am trying to add a constraint after the LP has been solved (using the optimal LP solution as a mechanism to devise this constraint). And I am adding it by this piece of code

432 SCIP_CONS * cons = nullptr;
433 namebuf.str("");
434 namebuf<<"cut_3_OR1";
435  SCIP_CALL(SCIPcreateConsLinear(scip, &cons, namebuf.str().c_str(), 0, nullptr, nullptr, -SCIPinfinity(scip), 1.0,   /* <= 1.0 constraint */
436                                    true,  /* initial  <= 0 */
437                                    false, /* separate */
438                                    true,  /* enforce */
439                                    true,  /* check */
440                                    true,  /* propagate */
441                                    false, /* local */
442                                    true,  /* modifiable */
443                                    false, /* dynamic */
444                                    false, /* removable */
445                                    false  /* stickingatnode */));

The code compiles fine but upon running the code, I get this error message

[src/scip/scip_cons.c:991] ERROR: invalid SCIP stage <10>
[src/scip/cons_linear.c:17695] ERROR: Error <-8> in function call
[src/Solver.h:445] ERROR: Error <-8> in function call
make: *** [run] Error 1

The code compiles and runs when I remove this constraint addition.

Could someone tell me what is wrong?

Leon · Accepted Answer · 2020-02-21 10:32:33Z

1

Stage 10 is SCIP_STAGE_SOLVED. You try to add a constraint after your problem is solved to optimality. Is the constraint that you want to add necessary? Then you might have to implement a constraint handler and add your constraint in the sepalp-callback of your handler. As an example, you could look at the TSP example in the SCIP documentation (it has a subtour-elimination constraint handler)

edited Feb 21, 2020 at 10:32

answered Feb 21, 2020 at 10:29

Leon

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5 Comments

Morpheus Over a year ago

Yes. It is necessary as it will increase the value of the lower bound. So I assume I have to add it how you have suggested. Are there any tutorials on how to do it? Thanks for your help.

Leon Over a year ago

There is also a section in the documentation about this: scip.zib.de/doc/html/CONS.php (and I edited my original post with an example)

Morpheus Over a year ago

I am not sure if I should ask this a separate question but I think I have a slightly related question. I want to add the aforementioned cut at my root node but I arrive at the root node after adding certain columns. I don't want to add any cuts during this column generation process. should I change anything significantly?

Leon Over a year ago

I assume you add your columns in a pricer plugin? You definitely should not add the cuts there. As I wrote, you should add the cuts in a constraint handler (or a separation routine if they are not model constraints)

Morpheus Over a year ago

Yes! I add columns using a pricer and I did implement the constraint handler (currently it does nothing as in i had not implemented it to add the cut but it does do some checks). I will ask it as a question so that it’s easier. Thanks

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