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Fix initial solution accepted index update in generate_initial() #339

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Fix initial solution accepted index update in generate_initial() #339

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4 changes: 2 additions & 2 deletions cpp/src/routing/diversity/diverse_solver.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -865,9 +865,9 @@ struct solve {
temp_pair.first = injection_info.solutions[next_injection];
if (!p->has_vehicle_fixed_costs()) {
auto injection_it = next_injection;
while (injection_it < injection_info.n_sol &&
while (injection_it < injection_info.n_sol-1 &&
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@hlinsen hlinsen Aug 22, 2025 •
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Thanks for reporting the bug and submitting the PR!
Could you please add the failing test here https://github.com/NVIDIA/cuopt/blob/branch-25.10/python/cuopt/cuopt/tests/routing/test_initial_solutions.py? Assuming you have the code ready.

Regarding the fix, after the change in your example we would be skipping sol[0] and add try to add it while omitting the target vehicle check.
We should set accepted in the for loop:

            while (injection_it < injection_info.n_sol &&
                   temp_pair.first.sol.get_n_routes() > target_vehicles_) {
              injection_info.accepted[injection_it] = 0;
              temp_pair.first = injection_info.solutions[injection_it++];
            }

And here check that next_injection < injection_info.n_sol as we could skip all solutions due to vehicle count and try to insert temp.first then write to accepted thus the out of bounds.

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@SomovMike SomovMike Sep 10, 2025

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Hi @hlinsen, thank you for your patience, and apologies for the delayed response.

Unfortunately, I don’t have a minimal failing test case available, as I encountered the issue on a large instance while working on my own implementation. I hope that’s not a problem, since the issue seems fairly clear from the code itself.

Regarding the fix, I think it depends on how you envision the logic of the algorithm. If the primary objective is to minimize the number of vehicles, and a solution with fewer vehicles has already been found, then it might make sense to skip all initial solutions with more vehicles.

That said, in my opinion, it could still be beneficial to include those initial solutions with more vehicles, since the crossover algorithm might be able to leverage them to generate improved solutions.

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@hlinsen hlinsen Sep 15, 2025

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In cuOpt we always assume minimization unless vehicle_fixed_costs are set or we use a fixed vehicle count in this case it does not change throughout the solve. Before the vehicle skip loop we are explicitly checking if vehicle fixed costs are set so following that logic we would not want to insert these vehicles at all.

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@hlinsen hlinsen Sep 26, 2025

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Hi @SomovMike , let me know if my comment makes sense. We should try to merge this asap since the fix is pretty small in any case :)

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@SomovMike SomovMike Sep 27, 2025

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Hi @hlinsen, okey, I got it. Your comment makes sense.

temp_pair.first.sol.get_n_routes() > target_vehicles_) {
temp_pair.first = injection_info.solutions[injection_it++];
temp_pair.first = injection_info.solutions[++injection_it];
}
next_injection = injection_it;
}
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