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cleaning up the inner tightening code

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Signed-off-by: Lev Nachmanson <levnach@hotmail.com>
This commit is contained in:
Lev Nachmanson 2025-03-20 17:22:23 -07:00 • committed by Lev Nachmanson
parent 8c96178c0b
commit f073da9edd
1 changed files with 33 additions and 21 deletions
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54
src/math/lp/dioph_eq.cpp
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@ -1666,10 +1666,11 @@ namespace lp {
TRACE("dio",
tout << "current " << (is_upper? "upper":"lower") << " bound for x" << j << ":"
<< rs << std::endl;);
rs = (rs - m_c) / g;
TRACE("dio", tout << "((rs - m_c) / g):" << rs << std::endl;);
if (!rs.is_int()) {
if (tighten_bound_kind(g, j, rs, is_upper))
mpq rs_mod_g = (rs - m_c) % g;
SASSERT(!rs_mod_g.is_neg() && rs_mod_g.is_int());
TRACE("dio", tout << "(rs - m_c) % g:" << rs_mod_g << std::endl;);
if (!rs_mod_g.is_zero()) {
if (tighten_bound_kind(g, j, rs, rs_mod_g, is_upper))
return lia_move::conflict;
} else {
TRACE("dio", tout << "no improvement in the bound\n";);
@ -1678,16 +1679,22 @@ namespace lp {
return lia_move::undef;
}
// returns true only on a conflict
bool tighten_bound_kind(const mpq& g, unsigned j, const mpq& ub, bool upper) {
// ub = (upper_bound(j) - m_c)/g.
// we have xj = t = g*t_+ m_c <= upper_bound(j), then
// t_ <= floor((upper_bound(j) - m_c)/g) = floor(ub)
//
// so xj = g*t_+m_c <= g*floor(ub) + m_c is new upper bound
// <= can be replaced with >= for lower bounds, with ceil instead of
// floor
mpq bound = g * (upper ? floor(ub) : ceil(ub)) + m_c;
// returns true only on a conflict
bool tighten_bound_kind(const mpq& g, unsigned j, const mpq& rs, const mpq& rs_mod_g, bool upper) {
// In case of an upper bound we have
// xj = t = g*t_+ m_c <= rs, also, by definition fo rs_mod_g, for some integer k holds rs - m_c = k*g + rs_mod_g.
// Then g*t_ <= rs - mc = k*g + rs_mod_g => g*t_ <= k*g = rs - m_c - rs_mod_g.
// Adding m_c to both parts gets us
// xj = g*t_ + m_c <= rs - rs_mod_g
// In case of a lower bound we have
// xj = t = g*t_+ m_c >= rs, also, by definition fo rs_mod_g, for some integer k holds rs - m_c = k*g + rs_mod_g.
// Then g*t_ >= rs - mc = k*g + rs_mod_g => g*t_ >= k*g = rs - m_c + g - rs_mod_g.
// Adding m_c to both parts gets us
// xj = g*t_ + m_c >= rs + g - rs_mod_g
mpq bound = upper ? rs - rs_mod_g : rs + g - rs_mod_g;
TRACE("dio", tout << "is upper:" << upper << std::endl;
tout << "new " << (upper ? "upper" : "lower")
<< " bound:" << bound << std::endl;);
@ -1696,15 +1703,20 @@ namespace lp {
(!upper && bound > lra.get_lower_bound(j).x));
lconstraint_kind kind = upper ? lconstraint_kind::LE : lconstraint_kind::GE;
u_dependency* dep = upper ? lra.get_column_upper_bound_witness(j) : lra.get_column_lower_bound_witness(j);
auto rs = open_fixed_from_ml(m_lspace);
auto fixed_part_of_the_term = open_fixed_from_ml(m_lspace);
// the right side is off by 1*j from m_espace
if (is_fixed(j))
rs.add(mpq(1), j);
for (const auto& p: rs) {
SASSERT(is_fixed(p.var()));
if ((p.coeff() / g).is_int())
continue; // explain todo!!!
fixed_part_of_the_term.add(mpq(1), j);
for (const auto& p: fixed_part_of_the_term) {
SASSERT(is_fixed(p.var()));
if ((p.coeff() % g).is_zero()) {
// we can skip thise dependency,
// because the monomial p.coeff()*p.var() is null by modulo g, and it does not matter that p.var() is fixed.
// We could have added p.coeff()*p.var() to t_, substructed the value of p.coeff()*p.var() from m_c and
// still get the same result.
TRACE("dio", tout << "skipped dep:\n"; print_deps(tout, lra.get_bound_constraint_witnesses_for_column(p.var())););
continue;
}
dep = lra.join_deps(dep, lra.get_bound_constraint_witnesses_for_column(p.var()));
}
TRACE("dio", tout << "jterm:";