Is there a way to save the cutting planes from SCIP?

Question

I am working on using SCIP to generate cutting planes for my project. I am doing so using a C++ code directly with default plugins included, modified from scip/examples/MIPsolver/src/cppmain. However the array of cutting planes is not saved. The program will be run using the command

./scipplanes [problem file]

The affected part of my program is shown below:

/*******************
    * Problem Presolving *
    *******************/

   /* Presolve problem */
   std::cout << "=============" << std::endl;
   std::cout << "Presolve problem" << std::endl;
   std::cout << "=============" << std::endl;
   SCIP_CALL( SCIPpresolve(scip) ); //Presolve to simplify the problem
   SCIP_CALL( SCIPsetRealParam(scip, "limits/time", 60) ); //Limit of solving time in seconds
   
   /*************************
    * Obtain cutting planes *
    *************************/
   std::cout << "=============" << std::endl;
   std::cout << "Obtaining cutting planes" << std::endl;
   std::cout << "=============" << std::endl;
   
   SCIP_ROW** allcuts; //Because SCIPgetCuts outputs this kind of data (memory address/pointer) 
   int n_cuts; //For for loop iteration
   
   SCIP_CALL( SCIPsolve(scip) );
   allcuts = SCIPgetCuts(scip); /*Documentation says that this outputs the array of cuts currently stored in the separation storage, 
                                   in the form of a memory address of pointer of SCIP_ROW** */
   std::cout << "allcuts is " << allcuts << std::endl;
   n_cuts = SCIPgetNCuts(scip);
   std::cout << "n_cuts is " << n_cuts << std::endl;

When I ran my code, I obtain n_cuts = 0, but the table of statistics shows :

time | node  | left  |LP iter|LP it/n|mem/heur|mdpt |vars |cons |rows |cuts |sepa|confs|strbr|  dualbound   | primalbound  |  gap   | compl.
60.0s|     1 |     0 | 33295 |     - |   333M |   0 |1164 |  39k|  39k| 120 | 10 |  19 |   0 | 0.000000e+00 |      --      |    Inf | unknown

There are 120 cuts. I have double checked by running the SCIP binary and using presolve and optimize with a time limit of 60s. The results are the same when display statistics is used.

I have also tried to iterate through allcuts by doing SCIPprintRow(scip, *allcuts, NULL); , but got a segmentation fault.

Thus, I have no idea why the cutting planes are not saved. Would it be possible to offer me some advice on how to solve this problem? Thank you.

score 1 · Answer 1 · answered Feb 11 '22 at 10:46

I'm pretty sure that all cuts will be freed after the solve is finished (and in any case, SCIP will remove rows from time to time). If you want all the cuts that were used at any point during the solve, you should write an event handler (with event type SCIP_EVENTTYPE_ROWEVENT) that you can use to print the rows with SCIPprintRow)

There is an example of how to write your own event handler in the examples subdirectory.

Is there a way to save the cutting planes from SCIP?

1 Answers1