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cheap_eqs
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Signed-off-by: Lev Nachmanson <levnach@hotmail.com>
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@levnach
levnach committed Jun 20, 2020
1 parent b5fc963 commit c2cead4
Showing 1 changed file with 69 additions and 67 deletions.
136 changes: 69 additions & 67 deletions src/math/lp/lp_bound_propagator.h
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Expand Up @@ -24,7 +24,7 @@ class lp_bound_propagator {
// and u, v reference the same column
class vertex {
unsigned m_row;
unsigned m_index; // in the row
unsigned m_column; // in the row
ptr_vector<vertex> m_children;
mpq m_offset; // offset from parent (parent - child = offset)
vertex* m_parent;
Expand All @@ -33,14 +33,14 @@ class lp_bound_propagator {
public:
vertex() {}
vertex(unsigned row,
unsigned index,
unsigned column,
const mpq & offset) :
m_row(row),
m_index(index),
m_column(column),
m_offset(offset),
m_parent(nullptr),
m_level(0) {}
unsigned index() const { return m_index; }
unsigned column() const { return m_column; }
unsigned row() const { return m_row; }
vertex* parent() const { return m_parent; }
unsigned level() const { return m_level; }
Expand All @@ -53,11 +53,11 @@ class lp_bound_propagator {
}
const ptr_vector<vertex> & children() const { return m_children; }
std::ostream& print(std::ostream & out) const {
out << "row = " << m_row << ", m_index = " << m_index << ", parent = " << m_parent << " , offset = " << m_offset << ", level = " << m_level << "\n";;
out << "row = " << m_row << ", column = " << m_column << ", parent = " << m_parent << " , offset = " << m_offset << ", level = " << m_level << "\n";;
return out;
}
bool operator==(const vertex& o) const {
return m_row == o.m_row && m_index == o.m_index;
return m_row == o.m_row && m_column == o.m_column;
}
};
hashtable<unsigned, u_hash, u_eq> m_visited_rows;
Expand All @@ -73,14 +73,17 @@ class lp_bound_propagator {
// these maps map a column index to the corresponding index in ibounds
std::unordered_map<unsigned, unsigned> m_improved_lower_bounds;
std::unordered_map<unsigned, unsigned> m_improved_upper_bounds;
struct signed_index {
class signed_column {
bool m_sign;
unsigned m_index;
signed_index() : m_index(UINT_MAX) {}
bool not_set() const { return m_index == UINT_MAX; }
bool is_set() const { return m_index != UINT_MAX; }
unsigned m_column;
public:
signed_column() : m_column(UINT_MAX) {}
bool not_set() const { return m_column == UINT_MAX; }
bool is_set() const { return m_column != UINT_MAX; }
bool sign() const { return m_sign; }
unsigned index() const { return m_index; }
bool& sign() { return m_sign; }
unsigned column() const { return m_column; }
unsigned& column() { return m_column; }
};

T& m_imp;
Expand Down Expand Up @@ -216,58 +219,59 @@ class lp_bound_propagator {
return true;
}

bool set_sign_and_index(const mpq& c, signed_index& i, unsigned k) {
if (c.is_one()) {
i.m_sign = false;
i.m_index = k;

bool set_sign_and_column(signed_column& i, const row_cell<mpq> & c) {
if (c.coeff().is_one()) {
i.sign() = false;
i.column() = c.var();
return true;
}
if (c.is_minus_one()){
i.m_sign = true;
i.m_index = k;
else if (c.coeff().is_minus_one()){
i.sign() = true;
i.column() = c.var();
return true;
}
return false;
}

void try_add_equation_with_fixed_tables(vertex *v) {
SASSERT(m_fixed_vertex);
unsigned v_j = column(v);
unsigned v_j = v->column();
unsigned j;
if (!lp().find_in_fixed_tables(v->offset(), is_int(v_j), j))
return;
ptr_vector<vertex> path;
find_path_on_tree(path, v, m_fixed_vertex);
explanation ex = get_explanation_from_path(path);
explain_fixed_column(ex, j);
add_eq_on_columns(ex, v_j, column(v));
add_eq_on_columns(ex, j, v->column());
}



void create_root(unsigned row_index) {
SASSERT(!m_root && !m_fixed_vertex);
signed_index x, y;
signed_column x, y;
mpq offset;
if (!is_offset_row_tree(row_index, x, y, offset))
if (!is_tree_offset_row(row_index, x, y, offset))
return;
TRACE("cheap_eq", display_row_info(row_index, tout););
if (y.not_set()) {
m_root = alloc(vertex, row_index, x.m_index, offset);
m_root = alloc(vertex, row_index, x.column(), offset);
m_fixed_vertex = m_root;
return;
}

// create root with the offset zero
m_root = alloc(vertex, row_index, x.m_index, mpq(0));
m_root = alloc(vertex, row_index, x.column(), mpq(0));
// we have x + sign_y * y + offset = 0
// x.offset is set to zero as x plays the role of m_root
// if sign_y = true then y.offset() = offset + x.offset()
// else y.offset() = - offset - x.offset()
if (!y.m_sign)
if (!y.sign())
offset.neg();

vertex *v = alloc(vertex, row_index, y.m_index, offset);
vertex *v = alloc(vertex, row_index, y.column(), offset);
m_root->add_child(v);
}

Expand All @@ -277,46 +281,48 @@ class lp_bound_propagator {

// returns the vertex to start exploration from, or nullptr
vertex* add_child_from_row(unsigned row_index, vertex* parent) {
signed_index x, y;
signed_column x, y;
mpq offset;
if (!is_offset_row_tree(row_index, x, y, offset))
if (!is_tree_offset_row(row_index, x, y, offset))
return nullptr;
if (y.not_set()) {
SASSERT(column(parent) == column(row_index, x.m_index));
SASSERT(parent->column() == x.column());
if (m_fixed_vertex) {
vertex* v = alloc(vertex, row_index, x.m_index, - offset);
vertex* v = alloc(vertex, row_index, x.column(), - offset);
parent->add_child(v);
return v;
}
vertex *v = alloc(vertex, row_index, x.m_index, parent->offset());
vertex *v = alloc(vertex, row_index, x.column(), parent->offset());
m_fixed_vertex = v;
parent->add_child(v);
// need to shift the tree so v.offset() becomes equal to - offset
shift_offsets_by_delta(m_root, - offset - parent->offset());
return v;
}
SASSERT(x.is_set() && y.is_set());
if (column(parent) == column(row_index, x.index())) {
vertex *vx = alloc(vertex, row_index, x.index(), parent->offset());
if (parent->column() == x.column()) {
vertex *vx = alloc(vertex, row_index, x.column(), parent->offset());
// mpq x_c = rat_sign(x.sign());
// mpq y_c = rat_sign(y.sign());
// we have x_c*x + y_c*y + offset = 0
// y = - offset/y_c - ( x_c/y_c )vx.offset;
bool x_c_y_c = x.sign() ^ y.sign();
mpq y_offs = (y.sign()? offset: - offset) - (x_c_y_c? - vx->offset() : vx->offset());
vertex *vy = alloc(vertex, row_index, y.index(), y_offs);
vertex *vy = alloc(vertex, row_index, y.column(), y_offs);
parent->add_child(vx);
vx->add_child(vy);
return vy; // start exploring from vy
} else {
vertex *vy = alloc(vertex, row_index, y.index(), parent->offset());
SASSERT(parent->column() == y.column());
vertex *vy = alloc(vertex, row_index, y.column(), parent->offset());
// mpq x_c = rat_sign(x.sign());
// mpq y_c = rat_sign(y.sign());
// we have x_c*x + y_c*y + offset = 0
// x = - offset/x_c - ( y_c/x_c )vy.offset;
bool y_c_x_c = x.sign() ^ y.sign();
mpq x_offs = (x.sign()? offset: -offset) - (y_c_x_c? - vy->offset(): vy->offset());
vertex *vx = alloc(vertex, row_index, y.index(), x_offs);
vertex *vx = alloc(vertex, row_index, y.column(), x_offs);
parent->add_child(vy);
vy->add_child(vx);
return vx;
}
Expand All @@ -330,8 +336,8 @@ class lp_bound_propagator {
vertex *k; // the other vertex

if (m_offset_to_verts.find(v->offset(), k)) {
if (column(k) != column(v) &&
!is_equal(column(k),column(v)))
if (k->column() != v->column() &&
!is_equal(k->column(), v->column()))
report_eq(k, v);
} else {
TRACE("cheap_eq", tout << "registered offset " << v->offset() << " to " << v << "\n";);
Expand All @@ -340,7 +346,7 @@ class lp_bound_propagator {

if (m_fixed_vertex) {
unsigned j;
unsigned v_col = column(v);
unsigned v_col = v->column();
if (lp().find_in_fixed_tables(v->offset(), is_int(v_col), j)) {
if (j != v_col) {
explanation ex;
Expand All @@ -360,14 +366,13 @@ class lp_bound_propagator {
void clear_for_eq() {
m_visited_rows.reset();
m_visited_columns.reset();
m_offset_to_verts.reset();
m_root = nullptr;
}

// we have v_i and v_j, indices of vertices at the same offsets
void report_eq(vertex* v_i, vertex* v_j) {
SASSERT(v_i != v_j);
TRACE("cheap_eq", tout << column(v_i) << " = " << column(v_j) << "\nu = ";
TRACE("cheap_eq", tout << v_i->column() << " = " << v_j->column() << "\nu = ";
v_i->print(tout) << "\nv = "; v_j->print(tout) <<"\n";
display_row_of_vertex(v_i, tout);
display_row_of_vertex(v_j, tout);
Expand All @@ -380,19 +385,19 @@ class lp_bound_propagator {
display_row_of_vertex(k, tout);
});
lp::explanation exp = get_explanation_from_path(path);
add_eq_on_columns(exp, column(v_i), column(v_j));
add_eq_on_columns(exp, v_i->column(), v_j->column());
}

void add_eq_on_columns(const explanation& exp, lpvar v_i_col, lpvar v_j_col) {
SASSERT(v_i_col != v_j_col);
unsigned i_e = lp().column_to_reported_index(v_i_col);
unsigned j_e = lp().column_to_reported_index(v_j_col);
TRACE("cheap_eq", tout << "reporting eq " << i_e << ", " << j_e << "\n";
void add_eq_on_columns(const explanation& exp, lpvar j, lpvar k) {
SASSERT(j != k);
unsigned je = lp().column_to_reported_index(j);
unsigned ke = lp().column_to_reported_index(k);
TRACE("cheap_eq", tout << "reporting eq " << je << ", " << ke << "\n";
for (auto p : exp) {
lp().constraints().display(tout, [this](lpvar j) { return lp().get_variable_name(j);}, p.ci());
});

m_imp.add_eq(i_e, j_e, exp);
m_imp.add_eq(je, ke, exp);
}

/**
Expand Down Expand Up @@ -601,9 +606,6 @@ class lp_bound_propagator {
}
return out;
}
lpvar column(const vertex* v) const {
return lp().get_row(v->row())[v->index()].var();
}

void cheap_eq_tree(unsigned row_index) {
TRACE("cheap_eq", tout << "row_index = " << row_index << "\n";);
Expand All @@ -619,6 +621,7 @@ class lp_bound_propagator {
TRACE("cheap_eq", tout << "tree size = " << verts_size(););
delete_tree(m_root);
m_root = m_fixed_vertex = nullptr;
m_offset_to_verts.reset();
}

unsigned verts_size() const {
Expand Down Expand Up @@ -647,15 +650,14 @@ class lp_bound_propagator {
}

void go_over_vertex_column(vertex * v) {
lpvar j = column(v);
lpvar j = v->column();
if (!check_insert(m_visited_columns, j))
return;

for (const auto & c : lp().get_column(j)) {
unsigned row_index = c.var();
if (!check_insert(m_visited_rows, row_index))
continue;
m_visited_rows.insert(row_index);
vertex *u = add_child_from_row(row_index, v);
if (u) {
explore_under(u);
Expand Down Expand Up @@ -711,21 +713,21 @@ class lp_bound_propagator {
// Will return x such that x.m_sign = false.
// In case of only one non fixed column, and the function returns true,
// this column would be represened by x
bool is_offset_row_tree(
bool is_tree_offset_row(
unsigned row_index,
signed_index & x,
signed_index & y,
signed_column & x,
signed_column & y,
mpq& offset) {
const auto & row = lp().get_row(row_index);
for (unsigned k = 0; k < row.size(); k++) {
const auto& c = row[k];
if (column_is_fixed(c.var()))
continue;
if (x.m_index == UINT_MAX) {
if (!set_sign_and_index(c.coeff(), x, k))
if (x.not_set()) {
if (!set_sign_and_column(x, c))
return false;
} else if (y.m_index == UINT_MAX) {
if (!set_sign_and_index(c.coeff(), y, k))
} else if (y.not_set()) {
if (!set_sign_and_column(y, c))
return false;
} else
return false;
Expand All @@ -741,18 +743,18 @@ class lp_bound_propagator {
offset += c.coeff() * get_lower_bound_rational(c.var());
}
if (offset.is_zero() &&
x.is_set() && y.is_set() && (x.m_sign != y.m_sign) &&
!is_equal(row[x.m_index].var(), row[y.m_index].var())) {
x.is_set() && y.is_set() && (x.sign() != y.sign()) &&
!is_equal(x.column(), y.column())) {
lp::explanation ex;
explain_fixed_in_row(row_index, ex);
add_eq_on_columns(ex, row[x.m_index].var(), row[y.m_index].var());
add_eq_on_columns(ex, x.column(), y.column());
}

if (x.m_sign) {
if (x.sign()) {
// flip the signs
x.m_sign = false;
x.sign() = false;
if (y.is_set()) {
y.m_sign = !y.m_sign;
y.sign() = !y.sign();
}
offset.neg();
}
Expand Down

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