Fix bugs on empty problem and pre_process assignment #18
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akifcorduk
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@akifcorduk Does this also cover @hlinsen bug fix? |
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Yes, it should cover that. But i think @hlinsen should also review. Maybe there is some conflicts. |
hlinsen
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May 19, 2025
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lgtm. One small coding style comment.
rg20
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May 20, 2025
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/merge |
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There was a bug in pre_process_assignment function. During initial solve() we are doing preprocess and then trivial_presolve. That means, the free var replacements are added first then the variable eliminations are done. For that reason the user solution preprocessing should follow the same order.
The bug of set_solution is called multiple times in the tests if fixed: we should to pop the back solution after solution is being set, otherwise it will always be set.
The bug of he assignment resize is fixed: it should be called before the gather, if not the resize will enlarge it and it will have junk values, causing mismatch in objective costs and sometimes infeasible solutions.
This also changes a slight issue where we assign 2x for y and x for z when x is positive, for large initial values this might cause numerical issues, that's why we now assign x for y and 0 for z.
This PR also fixes the bug of empty solutions not being handled correctly after a presolve (previously we handled it only for trivial presolve).