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Don't remove empty columns with infinite bounds #287

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Merged
rapids-bot merged 2 commits into from
Aug 12, 2025
Merged

Don't remove empty columns with infinite bounds #287

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9a6714f
Don't remove empty columns with infinite bounds
chris-maes Aug 11, 2025
0c0cf43
Style fixes
chris-maes Aug 11, 2025
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20 changes: 12 additions & 8 deletions cpp/src/dual_simplex/presolve.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -165,19 +165,23 @@ i_t remove_empty_cols(lp_problem_t<i_t, f_t>& problem,
std::vector<i_t> col_marker(problem.num_cols);
i_t new_cols = 0;
for (i_t j = 0; j < problem.num_cols; ++j) {
bool remove_var = false;
if ((problem.A.col_start[j + 1] - problem.A.col_start[j]) == 0) {
col_marker[j] = 1;
presolve_info.removed_variables.push_back(j);
presolve_info.removed_reduced_costs.push_back(problem.objective[j]);
if (problem.objective[j] >= 0) {
if (problem.objective[j] >= 0 && problem.lower[j] > -inf) {
presolve_info.removed_values.push_back(problem.lower[j]);
problem.obj_constant += problem.objective[j] * problem.lower[j];
assert(problem.lower[j] > -inf);
} else {
remove_var = true;
} else if (problem.objective[j] <= 0 && problem.upper[j] < inf) {
presolve_info.removed_values.push_back(problem.upper[j]);
problem.obj_constant += problem.objective[j] * problem.upper[j];
assert(problem.upper[j] < inf);
remove_var = true;
}
}

if (remove_var) {
col_marker[j] = 1;
presolve_info.removed_variables.push_back(j);
presolve_info.removed_reduced_costs.push_back(problem.objective[j]);
} else {
col_marker[j] = 0;
new_cols++;
Expand Down Expand Up @@ -751,7 +755,7 @@ i_t presolve(const lp_problem_t<i_t, f_t>& original,
}
}
if (num_empty_cols > 0) {
settings.log.printf("Presolve removing %d empty cols\n", num_empty_cols);
settings.log.printf("Presolve attempt to remove %d empty cols\n", num_empty_cols);
remove_empty_cols(problem, num_empty_cols, presolve_info);
}

Expand Down