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lp: remove dio_calls_period linear recovery that defeats dio backoff

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The Diophantine-handler scheduler in int_solver applies an exponential
backoff: solve_dioph_eq() doubles dio_calls_period on every unproductive
(undef) dio call to "throttle dio scheduling on failure", letting the
solver escalate to Gomory cuts / branching once dio is persistently
unproductive.

should_solve_dioph_eq() additionally decreased dio_calls_period by a
fixed amount (dio_calls_period_decrease, default 2) on every final_check
where dio did not fire. Because non-firing calls vastly outnumber firing
calls once the period grows, this linear per-call decrease overwhelms the
geometric backoff and pins the period near its initial small value, so an
unproductive dio keeps firing and the handoff to Gomory/branching never
durably engages.

On the nonlinear mixed Int/Real benchmark iss-8418/3.smt2 this causes a
20s timeout where the instance was previously solved as sat. Removing the
linear recovery (and the now-unused dio_calls_period_decrease parameter)
restores the intended backoff; the benchmark is solved sat in ~0.03s. The
dio-before-Gomory ordering and the dio_gomory_enable_period gating are
left unchanged.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Lev Nachmanson 2026-06-27 01:25:14 -07:00 • committed by GitHub
parent 6a62a53181
commit 2d17f0428a
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GPG key ID: B5690EEEBB952194
4 changed files with 0 additions and 10 deletions
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5
src/math/lp/int_solver.cpp
View file

@ -245,11 +245,6 @@ namespace lp {
bool should_solve_dioph_eq() {
bool ret = lia.settings().dio() && hit_period(settings().dio_calls_period());
if (!ret && lia.settings().dio_calls_period() > m_initial_dio_calls_period) {
unsigned dec = settings().dio_calls_period_decrease();
unsigned& period = lia.settings().dio_calls_period();
period = period > m_initial_dio_calls_period + dec ? period - dec : m_initial_dio_calls_period;
}
return ret;
}

1
src/math/lp/lp_params_helper.pyg
View file

@ -9,7 +9,6 @@ def_module_params(module_name='lp',
('dio_cuts_enable_hnf', BOOL, True, 'enable hnf cuts together with Diophantine cuts, only relevant when dioph_eq is true'),
('dio_ignore_big_nums', BOOL, True, 'Ignore the terms with big numbers in the Diophantine handler, only relevant when dioph_eq is true'),
('dio_calls_period', UINT, 1, 'Period of calling the Diophantine handler in the final_check()'),
('dio_calls_period_decrease', UINT, 2, 'Amount by which dio_calls_period is decreased on each final_check() call where the Diophantine handler is not triggered, until it returns to its initial value'),
('dio_run_gcd', BOOL, False, 'Run the GCD heuristic if dio is on, if dio is disabled the option is not used'),
('lcube', BOOL, True, 'use the largest cube test for integer feasibility'),
('lcube_flips', UINT, 16, 'maximal number of coordinate flips when repairing the rounded largest cube center, only relevant when lcube is true'),

1
src/math/lp/lp_settings.cpp
View file

@ -43,7 +43,6 @@ void lp::lp_settings::updt_params(params_ref const& _p) {
m_dump_bound_lemmas = p.arith_dump_bound_lemmas();
m_dio_ignore_big_nums = lp_p.dio_ignore_big_nums();
m_dio_calls_period = lp_p.dio_calls_period();
m_dio_calls_period_decrease = lp_p.dio_calls_period_decrease();
m_dio_run_gcd = lp_p.dio_run_gcd();
m_random_hammers = lp_p.random_hammers();
m_lcube = lp_p.lcube();

3
src/math/lp/lp_settings.h
View file

@ -265,7 +265,6 @@ private:
bool m_dump_bound_lemmas = false;
bool m_dio_ignore_big_nums = false;
unsigned m_dio_calls_period = 4;
unsigned m_dio_calls_period_decrease = 2;
bool m_dio_run_gcd = true;
bool m_random_hammers = true;
bool m_lcube = true;
@ -275,8 +274,6 @@ public:
unsigned lcube_flips() const { return m_lcube_flips; }
unsigned dio_calls_period() const { return m_dio_calls_period; }
unsigned & dio_calls_period() { return m_dio_calls_period; }
unsigned dio_calls_period_decrease() const { return m_dio_calls_period_decrease; }
unsigned & dio_calls_period_decrease() { return m_dio_calls_period_decrease; }
bool random_hammers() const { return m_random_hammers; }
bool & random_hammers() { return m_random_hammers; }
bool print_external_var_name() const { return m_print_external_var_name; }