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Fix 2095 #2096

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jajhall wants to merge 3 commits into from
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Fix 2095 #2096

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40af840
Added assert to trap rowNz.index() < 0 in HPresolve::equalityRowAddi…
jajhall Dec 30, 2024
6d58001
Now adding singletons to matrix after using vector in HPresolve::equ…
jajhall Dec 31, 2024
9065007
Merge branch 'latest' into fix-2095
jajhall Dec 31, 2024
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23 changes: 19 additions & 4 deletions src/presolve/HPresolve.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6133,15 +6133,30 @@ HPresolve::Result HPresolve::equalityRowAddition(
HighsPostsolveStack& postsolve_stack, HighsInt stayrow, HighsInt removerow,
double scale, const HighsMatrixSlice<RowStorageFormat>& vector) {
postsolve_stack.equalityRowAddition(removerow, stayrow, scale, vector);
// As exposed by #2095, adding to the matrix in the loop can corrupt
// vector, so possiblt accumulate the addiitons and perform then
// when vector is no longer needed
std::vector<std::pair<HighsInt, double>> add_index_value;
const bool add_to_matrix_after = true;
for (const auto& rowNz : vector) {
assert(rowNz.index() >= 0);
HighsInt pos = findNonzero(removerow, rowNz.index());
if (pos != -1)
if (pos != -1) {
unlink(pos); // all common nonzeros are cancelled, as the rows are
// parallel
else // might introduce a singleton
addToMatrix(removerow, rowNz.index(), scale * rowNz.value());
} else { // might introduce a singleton
if (add_to_matrix_after) {
add_index_value.push_back(std::make_pair(rowNz.index(), rowNz.value()));
} else {
addToMatrix(removerow, rowNz.index(), scale * rowNz.value());
}
}
}
if (add_to_matrix_after) {
for (HighsInt iX = 0; iX < HighsInt(add_index_value.size()); iX++)
addToMatrix(removerow, add_index_value[iX].first,
scale * add_index_value[iX].second);
}

if (model->row_upper_[removerow] != kHighsInf)
model->row_upper_[removerow] =
double(model->row_upper_[removerow] +
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