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add var_factors

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Add routine to partially factor polynomials. It factors out variables.
This commit is contained in:
Nikolaj Bjorner 2022-07-14 11:06:43 -07:00
parent 981c82c814
commit 4a192850f2
3 changed files with 134 additions and 0 deletions
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72
src/math/dd/dd_pdd.cpp
View file

@ -1311,6 +1311,78 @@ namespace dd {
return m.mk_var(var())*h + l;
}
std::pair<unsigned_vector, pdd> pdd::var_factors() {
if (is_val())
return { unsigned_vector(), *this };
unsigned v = var();
if (lo().is_val()) {
if (!lo().is_zero())
return { unsigned_vector(), *this };
auto [vars, p] = hi().var_factors();
vars.push_back(v);
return {vars, p};
}
auto [lo_vars, q] = lo().var_factors();
if (lo_vars.empty())
return { unsigned_vector(), *this };
unsigned_vector lo_and_hi;
auto merge = [&](unsigned_vector& lo_vars, unsigned_vector& hi_vars) {
unsigned ir = 0, jr = 0;
for (unsigned i = 0, j = 0; i < lo_vars.size() || j < hi_vars.size(); ) {
if (i == lo_vars.size()) {
hi_vars[jr++] = hi_vars[j++];
continue;
}
if (j == hi_vars.size()) {
lo_vars[ir++] = lo_vars[i++];
continue;
}
if (lo_vars[i] == hi_vars[j]) {
lo_and_hi.push_back(lo_vars[i]);
++i;
++j;
continue;
}
unsigned lvl_lo = m.m_var2level[lo_vars[i]];
unsigned lvl_hi = m.m_var2level[hi_vars[j]];
if (lvl_lo > lvl_hi) {
hi_vars[jr++] = hi_vars[j++];
continue;
}
else {
lo_vars[ir++] = lo_vars[i++];
continue;
}
}
lo_vars.shrink(ir);
hi_vars.shrink(jr);
};
auto mul = [&](unsigned_vector const& vars, pdd p) {
for (auto v : vars)
p *= m.mk_var(v);
return p;
};
auto [hi_vars, p] = hi().var_factors();
if (lo_vars.back() == v) {
lo_vars.pop_back();
merge(lo_vars, hi_vars);
lo_and_hi.push_back(v);
return { lo_and_hi, mul(lo_vars, q) + mul(hi_vars, p) };
}
if (hi_vars.empty())
return { unsigned_vector(), *this };
merge(lo_vars, hi_vars);
hi_vars.push_back(v);
if (lo_and_hi.empty())
return { unsigned_vector(), *this };
else
return { lo_and_hi, mul(lo_vars, q) + mul(hi_vars, p) };
}
std::ostream& operator<<(std::ostream& out, pdd const& b) { return b.display(out); }

5
src/math/dd/dd_pdd.h
View file

@ -364,6 +364,11 @@ namespace dd {
bool different_leading_term(pdd const& other) const { return m.different_leading_term(*this, other); }
void factor(unsigned v, unsigned degree, pdd& lc, pdd& rest) { m.factor(*this, v, degree, lc, rest); }
/**
* \brief factor out variables
*/
std::pair<unsigned_vector, pdd> var_factors();
pdd subst_val(vector<std::pair<unsigned, rational>> const& s) const { return m.subst_val(*this, s); }
pdd subst_val(unsigned v, rational const& val) const { return m.subst_val(*this, v, val); }