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fix #6300
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several boundary cases with repeated rows being retired twice and non-termination for K = 1 where decomposition is just identity.
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@NikolajBjorner
NikolajBjorner committed Aug 25, 2022
1 parent fb8532b commit d975886
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Showing 2 changed files with 42 additions and 20 deletions.
45 changes: 34 additions & 11 deletions src/math/simplex/model_based_opt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -736,6 +736,8 @@ namespace opt {

void model_based_opt::normalize(unsigned row_id) {
row& r = m_rows[row_id];
if (!r.m_alive)
return;
if (r.m_vars.empty()) {
retire_row(row_id);
return;
Expand Down Expand Up @@ -934,6 +936,7 @@ namespace opt {
else {
row_id = m_retired_rows.back();
m_retired_rows.pop_back();
SASSERT(!m_rows[row_id].m_alive);
m_rows[row_id].reset();
m_rows[row_id].m_alive = true;
}
Expand Down Expand Up @@ -995,17 +998,18 @@ namespace opt {
return v;
}

void model_based_opt::add_constraint(vector<var> const& coeffs, rational const& c, rational const& m, ineq_type rel, unsigned id) {
unsigned model_based_opt::add_constraint(vector<var> const& coeffs, rational const& c, rational const& m, ineq_type rel, unsigned id) {
auto const& r = m_rows.back();
if (r.m_vars == coeffs && r.m_coeff == c && r.m_mod == m && r.m_type == rel && r.m_id == id && r.m_alive)
return;
return m_rows.size() - 1;
unsigned row_id = new_row();
set_row(row_id, coeffs, c, m, rel);
m_rows[row_id].m_id = id;
for (var const& coeff : coeffs)
m_var2row_ids[coeff.m_id].push_back(row_id);
SASSERT(invariant(row_id, m_rows[row_id]));
normalize(row_id);
return row_id;
}

void model_based_opt::set_objective(vector<var> const& coeffs, rational const& c) {
Expand Down Expand Up @@ -1236,10 +1240,15 @@ namespace opt {
unsigned y = add_var(y_value, true);

uint_set visited;
unsigned j = 0;
for (unsigned ri : mod_rows) {
if (visited.contains(ri))
continue;
m_rows[ri].m_alive = false;
visited.insert(ri);
mod_rows[j++] = ri;
}
mod_rows.shrink(j);

// replace x by K*y + z in other rows.
for (unsigned ri : m_var2row_ids[x]) {
Expand All @@ -1266,11 +1275,12 @@ namespace opt {

unsigned w = UINT_MAX;
rational offset(0);
if (coeffs.empty())
if (coeffs.empty() || K == 1)
offset = mod(coeff, K);
else
w = add_mod(coeffs, coeff, K);


rational w_value = w == UINT_MAX ? offset : m_var2value[w];

// add v = a*z + w - V, for k = (a*z_value + w_value) div K
Expand All @@ -1284,8 +1294,7 @@ namespace opt {
add_lower_bound(v, rational::zero());
add_upper_bound(v, K - 1);

// allow to recycle row.
m_retired_rows.push_back(ri);
retire_row(ri);

project(v, false);
}
Expand Down Expand Up @@ -1341,12 +1350,17 @@ namespace opt {
unsigned y = add_var(y_value, true);

uint_set visited;
unsigned j = 0;
for (unsigned ri : div_rows) {
if (visited.contains(ri))
continue;
row& r = m_rows[ri];
mul(ri, K / r.m_mod);
r.m_alive = false;
visited.insert(ri);
div_rows[j++] = ri;
}
div_rows.shrink(j);

// replace x by K*y + z in other rows.
for (unsigned ri : m_var2row_ids[x]) {
Expand Down Expand Up @@ -1375,9 +1389,11 @@ namespace opt {
rational coeff = m_rows[ri].m_coeff;
unsigned w = UINT_MAX;
rational offset(0);
if (coeffs.empty())
if (K == 1)
offset = coeff;
else if (coeffs.empty())
offset = div(coeff, K);
else
else
w = add_div(coeffs, coeff, K);

//
Expand Down Expand Up @@ -1412,28 +1428,35 @@ namespace opt {
vector<var> div_coeffs;
div_coeffs.push_back(var(v, rational::minus_one()));
div_coeffs.push_back(var(y, a));
if (w != UINT_MAX) div_coeffs.push_back(var(w, rational::one()));
if (w != UINT_MAX)
div_coeffs.push_back(var(w, rational::one()));
else if (K == 1)
div_coeffs.append(coeffs);
add_constraint(div_coeffs, k + offset, t_eq);

unsigned u = UINT_MAX;
offset = 0;
if (coeffs.empty())
if (K == 1)
offset = 0;
else if (coeffs.empty())
offset = mod(coeff, K);
else
u = add_mod(coeffs, coeff, K);


// add a*z + (b mod K) < (k + 1)*K
vector<var> bound_coeffs;
bound_coeffs.push_back(var(z, a));
if (u != UINT_MAX) bound_coeffs.push_back(var(u, rational::one()));
if (u != UINT_MAX)
bound_coeffs.push_back(var(u, rational::one()));
add_constraint(bound_coeffs, 1 - K * (k + 1) + offset, t_le);

// add k*K <= az + (b mod K)
for (auto& c : bound_coeffs)
c.m_coeff.neg();
add_constraint(bound_coeffs, k * K - offset, t_le);
// allow to recycle row.
m_retired_rows.push_back(ri);
retire_row(ri);
project(v, false);
}

Expand Down
17 changes: 8 additions & 9 deletions src/math/simplex/model_based_opt.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -60,14 +60,13 @@ namespace opt {
}
};
struct row {
row(): m_type(t_le), m_value(0), m_alive(false) {}
vector<var> m_vars; // variables with coefficients
rational m_coeff; // constant in inequality
rational m_mod; // value the term divide
ineq_type m_type; // inequality type
rational m_value; // value of m_vars + m_coeff under interpretation of m_var2value.
bool m_alive; // rows can be marked dead if they have been processed.
unsigned m_id; // variable defined by row (used for mod_t and div_t)
vector<var> m_vars; // variables with coefficients
rational m_coeff = rational::zero(); // constant in inequality
rational m_mod = rational::zero(); // value the term divide
ineq_type m_type = t_le; // inequality type
rational m_value = rational::zero(); // value of m_vars + m_coeff under interpretation of m_var2value.
bool m_alive = false; // rows can be marked dead if they have been processed.
unsigned m_id = UINT_MAX; // variable defined by row (used for mod_t and div_t)
void reset() { m_vars.reset(); m_coeff.reset(); m_value.reset(); }

row& normalize();
Expand Down Expand Up @@ -139,7 +138,7 @@ namespace opt {

void add_upper_bound(unsigned x, rational const& hi);

void add_constraint(vector<var> const& coeffs, rational const& c, rational const& m, ineq_type r, unsigned id);
unsigned add_constraint(vector<var> const& coeffs, rational const& c, rational const& m, ineq_type r, unsigned id);

void replace_var(unsigned row_id, unsigned x, rational const& A, unsigned y, rational const& B);

Expand Down

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