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Fix a segfault on bnatt500 due to small mu leading to inf/nan #254

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Merged
rapids-bot merged 1 commit into from
Aug 5, 2025
Merged

Fix a segfault on bnatt500 due to small mu leading to inf/nan #254

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22 changes: 16 additions & 6 deletions cpp/src/dual_simplex/basis_updates.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1872,6 +1872,11 @@ i_t basis_update_mpf_t<i_t, f_t>::update(const std::vector<f_t>& utilde,
S_.x.data() + S_.col_start[S_start + 1],
v_nz);

if (std::abs(mu) < 1e-13) {
// Force a refactor. Otherwise we will get numerical issues when dividing by mu.
return 1;
}

#ifdef CHECK_MU
const f_t mu_check = 1.0 + dot<i_t, f_t>(etilde, u);
printf("Update: mu %e mu_check %e diff %e\n", mu, mu_check, std::abs(mu - mu_check));
Expand Down Expand Up @@ -1924,12 +1929,17 @@ i_t basis_update_mpf_t<i_t, f_t>::update(const sparse_vector_t<i_t, f_t>& utilde
S_.append_column(etilde);

// Compute mu = 1 + v^T * u
mu_values_.push_back(1.0 + sparse_dot(S_.i.data() + S_.col_start[S_start],
S_.x.data() + S_.col_start[S_start],
S_.col_start[S_start + 1] - S_.col_start[S_start],
S_.i.data() + S_.col_start[S_start + 1],
S_.x.data() + S_.col_start[S_start + 1],
S_.col_start[S_start + 2] - S_.col_start[S_start + 1]));
const f_t mu = 1.0 + sparse_dot(S_.i.data() + S_.col_start[S_start],
S_.x.data() + S_.col_start[S_start],
S_.col_start[S_start + 1] - S_.col_start[S_start],
S_.i.data() + S_.col_start[S_start + 1],
S_.x.data() + S_.col_start[S_start + 1],
S_.col_start[S_start + 2] - S_.col_start[S_start + 1]);
if (std::abs(mu) < 1e-13) {
// Force a refactor. Otherwise we will get numerical issues when dividing by mu.
return 1;
}
mu_values_.push_back(mu);
// Clear the workspace
for (i_t k = 0; k < nz; ++k) {
const i_t i = xi_workspace_[m + k];
Expand Down