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cautious remove_basis

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Signed-off-by: Lev Nachmanson <levnach@hotmail.com>
This commit is contained in:
Lev Nachmanson 2020-05-28 11:47:11 -07:00
parent 91d9b0319e
commit a6040a1f3d
5 changed files with 50 additions and 1 deletions
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34
src/math/lp/lar_solver.cpp
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@ -565,6 +565,40 @@ bool lar_solver::remove_from_basis(unsigned j) {
return m_mpq_lar_core_solver.m_r_solver.remove_from_basis(j);
}
// val is the new value to be assigned to x[j]
// return true iff can find a new basic column that would be feasible
// after the pivoting
bool lar_solver::remove_from_basis(unsigned basic_j, const mpq& val) {
SASSERT(is_base(basic_j));
impq del(0);
const auto& slv = m_mpq_lar_core_solver.m_r_solver;
bool grow = val < get_column_value(basic_j).x; // grow = true means that the monomial of the pivoted var has to grow
for (auto &c : A_r().m_rows[row_of_basic_column(basic_j)]) {
lpvar j = c.var();
if (j == basic_j) {
SASSERT(c.coeff().is_one());
continue;
}
bool can_pivot = column_is_free(j);
if (!can_pivot &&
((grow && slv.monoid_can_increase(c))|| (!grow && slv.monoid_can_decrease(c)))) {
if (del.is_zero())
del = impq(val) - get_column_value(basic_j);
impq j_val = get_column_value(j) - del / c.coeff();
if (inside_bounds(j, j_val))
can_pivot = true;
}
if (can_pivot) {
pivot_column_tableau(c.var(), row_of_basic_column(basic_j));
return true;
}
}
return false;
}
lar_term lar_solver::get_term_to_maximize(unsigned j_or_term) const {
if (tv::is_term(j_or_term)) {
return get_term(j_or_term);