[SCIP] creating and checking solution in the original space

[Ambros Gleixner]

Dear Marko,

Sorry for the delayed reply.  From your description I have no good idea 
what could go wrong.  Your workflow should be fine.  Could it be that 
you use SCIP_VAR* pointers for transformed problem variables when 
calling SCIPsetSolVal() on the original solution?  I suppose you have 
run the code in debug mode and no asserts came up?

Best,
Ambros



Am 13.10.22 um 09:31 schrieb HORVÁTH Markó:
> Hi all,
> 
> I'm working on a project, where we need to solve a task assignment-like 
> problem. Briefly,
> - we have x-variables to assign quantities to operators in a planning 
> horizon,
> - we have y-variables to aggregate certain x-variables (i.e., y = x + x 
> + ... + x),
> - we have surplus/backlog variables to handle stock level (i.e., y(t) + 
> s(t-1) + b(t) = s(t) + b(t-1) + demand(t)),
> - and we have a lot of knapsack constraints on x-variables which make 
> the problem hard.
> 
> Because on bigger instances SCIP hardly finds an integer feasible 
> solution, I'm about to create a primal heuristic method. That is, I want 
> to round down the LP values of the x-variables, and adjust the other 
> variables to satisfy the aggregation and balance equations.
> 
> I want to work on original variables, because preprocessing may change 
> variable bounds, and the created solution would be infeasible (and I 
> also should deal with multi-agregated variables, etc.). It is not 
> problem for me, if I cannot store the solution in SCIP, but I want to 
> check its feasiblity.
> 1) I created a primal heuristic class from *scip::ObjHeur*.
> 2) I got the current LP solution via *SCIPlinkLPSol*.
> 3) I created a new primal solution in the original space via 
> *SCIPcreateOrigSol*.
> 4) Then, for (original) x-variables I do the rounding: *SCIPgetSolVal -> 
> SCIPfloor -> SCIPsetSolVal*. (And for all the other variables I also set 
> the adjusted value via SCIPsetSolVal).
> 5) Unfortunately (for the second time), *SCIPcheckSolOrig**raises an 
> error*: solution violates original bounds of variable <t_x_47_128_2> 
> [-0,0] solution value <15>
> 
> But, when I check the solution value of the original/transformed 
> variables x_47_128_2/t_x_47_128_2 in the new solution, these are not 15, 
> but 0.
> 
> So, could you please help me if my approach is good or not, and if yes, 
> what can cause this checking error?
> 
> Best regards,
> Marko
> 
> 
> 
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> https://listserv.zib.de/mailman/listinfo/scip