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handle root expressions, and checking exponentiation with nlsat

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this one is for you @matthai
This commit is contained in:
Nikolaj Bjorner 2025-04-22 13:47:38 -07:00
parent 2fe2735b5e
commit ff920ba51b
2 changed files with 131 additions and 61 deletions
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180
src/math/lp/nla_powers.cpp
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@ -83,110 +83,172 @@ namespace nla {
core& c = m_core;
if (x == null_lpvar || y == null_lpvar || r == null_lpvar)
return l_undef;
if (c.lra.column_has_term(x) || c.lra.column_has_term(y) || c.lra.column_has_term(r))
return l_undef;
if (c.use_nra_model())
return l_undef;
auto xval = c.val(x);
auto yval = c.val(y);
auto rval = c.val(r);
// if (c.lra.column_has_term(x) || c.lra.column_has_term(y) || c.lra.column_has_term(r))
// return l_undef;
lemmas.reset();
if (xval != 0 && yval == 0 && rval != 1) {
auto x_exp_0 = [&]() {
new_lemma lemma(c, "x != 0 => x^0 = 1");
lemma |= ineq(x, llc::EQ, rational::zero());
lemma |= ineq(y, llc::NE, rational::zero());
lemma |= ineq(r, llc::EQ, rational::one());
return l_false;
}
};
if (xval == 0 && yval != 0 && rval != 0) {
auto zero_exp_y = [&]() {
new_lemma lemma(c, "y != 0 => 0^y = 0");
lemma |= ineq(x, llc::NE, rational::zero());
lemma |= ineq(y, llc::EQ, rational::zero());
lemma |= ineq(r, llc::EQ, rational::zero());
return l_false;
}
};
if (xval > 0 && rval <= 0) {
auto x_gt_0 = [&]() {
new_lemma lemma(c, "x > 0 => x^y > 0");
lemma |= ineq(x, llc::LE, rational::zero());
lemma |= ineq(r, llc::GT, rational::zero());
return l_false;
}
};
if (xval > 1 && yval < 0 && rval >= 1) {
auto y_lt_1 = [&]() {
new_lemma lemma(c, "x > 1, y < 0 => x^y < 1");
lemma |= ineq(x, llc::LE, rational::one());
lemma |= ineq(y, llc::GE, rational::zero());
lemma |= ineq(r, llc::LT, rational::one());
return l_false;
}
};
if (xval > 1 && yval > 0 && rval <= 1) {
auto y_gt_1 = [&]() {
new_lemma lemma(c, "x > 1, y > 0 => x^y > 1");
lemma |= ineq(x, llc::LE, rational::one());
lemma |= ineq(y, llc::LE, rational::zero());
lemma |= ineq(r, llc::GT, rational::one());
return l_false;
}
};
if (xval >= 3 && yval != 0 && rval <= yval + 1) {
auto x_ge_3 = [&]() {
new_lemma lemma(c, "x >= 3, y != 0 => x^y > ln(x)y + 1");
lemma |= ineq(x, llc::LT, rational(3));
lemma |= ineq(y, llc::EQ, rational::zero());
lemma |= ineq(lp::lar_term(r, rational::minus_one(), y), llc::GT, rational::one());
return l_false;
};
bool use_rational = !c.use_nra_model();
rational xval, yval, rval;
if (use_rational) {
xval = c.val(x);
yval = c.val(y);
rval = c.val(r);
}
else {
auto& am = c.m_nra.am();
if (am.is_rational(c.m_nra.value(x)) &&
am.is_rational(c.m_nra.value(y)) &&
am.is_rational(c.m_nra.value(r))) {
am.to_rational(c.m_nra.value(x), xval);
am.to_rational(c.m_nra.value(y), yval);
am.to_rational(c.m_nra.value(r), rval);
use_rational = true;
}
}
if (xval > 0 && yval.is_unsigned()) {
auto r2val = power(xval, yval.get_unsigned());
if (rval == r2val)
return l_true;
if (c.random() % 2 == 0) {
new_lemma lemma(c, "x == x0, y == y0 => r = x0^y0");
lemma |= ineq(x, llc::NE, xval);
lemma |= ineq(y, llc::NE, yval);
lemma |= ineq(r, llc::EQ, r2val);
return l_false;
if (use_rational) {
auto xval = c.val(x);
auto yval = c.val(y);
auto rval = c.val(r);
if (xval != 0 && yval == 0 && rval != 1)
return x_exp_0();
else if (xval == 0 && yval != 0 && rval != 0)
return zero_exp_y();
else if (xval > 0 && rval <= 0)
return x_gt_0();
else if (xval > 1 && yval < 0 && rval >= 1)
return y_lt_1();
else if (xval > 1 && yval > 0 && rval <= 1)
return y_gt_1();
else if (xval >= 3 && yval != 0 && rval <= yval + 1)
return x_ge_3();
else if (xval > 0 && yval.is_unsigned()) {
auto r2val = power(xval, yval.get_unsigned());
if (rval == r2val)
return l_true;
if (c.random() % 2 == 0) {
new_lemma lemma(c, "x == x0, y == y0 => r = x0^y0");
lemma |= ineq(x, llc::NE, xval);
lemma |= ineq(y, llc::NE, yval);
lemma |= ineq(r, llc::EQ, r2val);
return l_false;
}
if (yval > 0 && r2val > rval) {
new_lemma lemma(c, "x >= x0 > 0, y >= y0 > 0 => r >= x0^y0");
lemma |= ineq(x, llc::LT, xval);
lemma |= ineq(y, llc::LT, yval);
lemma |= ineq(r, llc::GE, r2val);
return l_false;
}
if (r2val < rval) {
new_lemma lemma(c, "0 < x <= x0, y <= y0 => r <= x0^y0");
lemma |= ineq(x, llc::LE, rational::zero());
lemma |= ineq(x, llc::GT, xval);
lemma |= ineq(y, llc::GT, yval);
lemma |= ineq(r, llc::LE, r2val);
return l_false;
}
}
if (yval > 0 && r2val > rval) {
new_lemma lemma(c, "x >= x0 > 0, y >= y0 > 0 => r >= x0^y0");
lemma |= ineq(x, llc::LT, xval);
lemma |= ineq(y, llc::LT, yval);
lemma |= ineq(r, llc::GE, r2val);
return l_false;
}
if (r2val < rval) {
new_lemma lemma(c, "0 < x <= x0, y <= y0 => r <= x0^y0");
lemma |= ineq(x, llc::LE, rational::zero());
lemma |= ineq(x, llc::GT, xval);
lemma |= ineq(y, llc::GT, yval);
lemma |= ineq(r, llc::LE, r2val);
return l_false;
if (xval > 0 && yval > 0 && !yval.is_int()) {
auto ynum = numerator(yval);
auto yden = denominator(yval);
// r = x^{yn/yd}
// <=>
// r^yd = x^yn
if (ynum.is_unsigned() && yden.is_unsigned()) {
auto ryd = power(rval, yden.get_unsigned());
auto xyn = power(xval, ynum.get_unsigned());
if (ryd == xyn)
return l_true;
}
}
}
if (xval > 0 && yval > 0 && !yval.is_int()) {
auto ynum = numerator(yval);
auto yden = denominator(yval);
if (!ynum.is_unsigned())
return l_undef;
if (!yden.is_unsigned())
return l_undef;
// r = x^{yn/yd}
// <=>
// r^yd = x^yn
auto ryd = power(rval, yden.get_unsigned());
auto xyn = power(xval, ynum.get_unsigned());
if (ryd == xyn)
return l_true;
if (!use_rational) {
auto& am = c.m_nra.am();
scoped_anum xval(am), yval(am), rval(am);
am.set(xval, c.m_nra.value(x));
am.set(yval, c.m_nra.value(y));
am.set(rval, c.m_nra.value(r));
if (xval != 0 && yval == 0 && rval != 1)
return x_exp_0();
else if (xval == 0 && yval != 0 && rval != 0)
return zero_exp_y();
else if (xval > 0 && rval <= 0)
return x_gt_0();
else if (xval > 1 && yval < 0 && rval >= 1)
return y_lt_1();
else if (xval > 1 && yval > 0 && rval <= 1)
return y_gt_1();
else if (xval >= 3 && yval != 0 && rval <= yval + 1)
return x_ge_3();
else if (xval > 0 && yval > 0 && am.is_rational(yval)) {
rational yr;
am.to_rational(yval, yr);
auto ynum = numerator(yr);
auto yden = denominator(yr);
// r = x^{yn/yd}
// <=>
// r^yd = x^yn
if (ynum.is_unsigned() && yden.is_unsigned()) {
am.set(rval, power(rval, yden.get_unsigned()));
am.set(xval, power(xval, ynum.get_unsigned()));
if (rval == xval)
return l_true;
}
}
}
return l_undef;
}
}

8
src/smt/theory_lra.cpp
View file

@ -1099,6 +1099,14 @@ public:
expr_ref zero(a.mk_real(0), m);
mk_axiom(~mk_literal(a.mk_le(p, zero)));
}
if (a.is_extended_numeral(y, r) && r > 0) {
// r is 1/n then x >= 0 => x = p^n
if (numerator(r) == 1 && denominator(r) > 1) {
expr_ref x_ge_0(a.mk_ge(x, a.mk_real(0)), m);
expr_ref x_eq_pn(a.mk_eq(x, a.mk_power(p, a.mk_real(denominator(r)))), m);
mk_axiom(~mk_literal(x_ge_0), mk_literal(x_eq_pn));
}
}
bool can_be_underspecified = false;
if (a.is_numeral(x, r) && r == 0 && (!a.is_numeral(y, r) || r == 0))
can_be_underspecified = true;