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fixing optimizer for multi-objectives and epsilon

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2013-10-22 10:36:13 +08:00
parent 3441fc2942
commit 36d7948399
6 changed files with 127 additions and 60 deletions
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87
src/opt/optimize_objectives.cpp
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@ -15,6 +15,26 @@ Author:
Notes:
Suppose we obtain solution t1 = k1, ..., tn = kn-epsilon
Assert:
t1 > k1 \/ t2 > k2 \/ ... \/ tn >= kn
If this solution is satisfiable, then for each t_i, maximize the
assignment and assert the new frontier.
Claim: we don't necessarily have to freeze assignments of
t_i when optimizing assignment for t_j
because the state will always satisfy the disjunction.
If one of the k_i is unbounded, then omit a disjunction for it.
Claim: the end result (when the constraints are no longer feasible)
is Pareto optimal, but convergence will probably not be as fast
as when fixing one parameter at a time.
E.g., a different approach is first to find a global maximal for one
variable. Then add a method to "freeze" that variable at the extremum if it is finite.
To do this, add lower and upper bounds for that variable using infinitesimals.
If the variable is unbounded, then this is of course not sufficient by itself.
--*/
#ifndef _OPT_OBJECTIVE_H_
@ -31,13 +51,14 @@ namespace opt {
*/
lbool mathsat_style_opt(
opt_solver& s,
app_ref_vector& objectives,
svector<bool> const& is_max,
app_ref_vector const& objectives,
vector<inf_eps_rational<inf_rational> >& values)
{
SASSERT(is_max.size() == objectives.size());
ast_manager& m = objectives.get_manager();
arith_util autil(m);
// First check_sat call for initialize theories
s.reset_objectives();
// First check_sat call to initialize theories
lbool is_sat = s.check_sat(0, 0);
if (is_sat == l_false) {
return is_sat;
@ -45,38 +66,41 @@ namespace opt {
s.push();
// Temporarily ignore the assertion to run the first objective function
//SASSERT(is_max.size() == 1);
ast_manager& m = objectives.get_manager();
arith_util autil(m);
bool ismax = is_max[0];
app_ref objective_var(m), objective_term(m), obj_eq(m);
objective_term = ismax?objectives[0].get():autil.mk_uminus(objectives[0].get());
sort* srt = m.get_sort(objective_term);
objective_var = m.mk_fresh_const("objective", srt);
obj_eq = autil.mk_eq(objective_var, objective_term);
s.assert_expr(obj_eq);
s.set_objective(objective_var); // NSB review: I would change signature of set_objective to take is_max and decide whether to add equation.
// Otherwise, the difference logic backends will not work.
s.toggle_objective(true);
opt_solver::toggle_objective _t(s, true);
for (unsigned i = 0; i < objectives.size(); ++i) {
s.add_objective(objectives[i]);
}
is_sat = s.check_sat(0, 0);
while (is_sat == l_true) {
// Extract values for objectives
inf_eps_rational<inf_rational> val;
val = ismax ? s.get_objective_value() : -s.get_objective_value();
// Check whether objective is unbounded
values.reset();
values.push_back(val);
values.append(s.get_objective_values());
IF_VERBOSE(1,
for (unsigned i = 0; i < values.size(); ++i) {
verbose_stream() << values[i] << " ";
}
verbose_stream() << "\n";);
expr_ref_vector disj(m);
expr_ref constraint(m), num(m);
for (unsigned i = 0; i < objectives.size(); ++i) {
if (!val.get_infinity().is_zero()) {
break;
if (!values[i].get_infinity().is_zero()) {
continue;
}
num = autil.mk_numeral(values[i].get_rational(), m.get_sort(objectives[i]));
SASSERT(values[i].get_infinitesimal().is_nonpos());
if (values[i].get_infinitesimal().is_neg()) {
disj.push_back(autil.mk_ge(objectives[i], num));
}
else {
disj.push_back(autil.mk_gt(objectives[i], num));
}
}
expr_ref constraint(m);
constraint = autil.mk_gt(objective_term, autil.mk_numeral(val.get_rational(), srt));
constraint = m.mk_or(disj.size(), disj.c_ptr());
s.assert_expr(constraint);
is_sat = s.check_sat(0, 0);
}
@ -86,7 +110,6 @@ namespace opt {
if (is_sat == l_undef) {
return is_sat;
}
//SASSERT(is_sat == l_false); // NSB review: not really water-tight with cancellation and with infinitesimal solutions.
return l_true;
}
@ -96,9 +119,9 @@ namespace opt {
*/
lbool optimize_objectives(opt_solver& s,
app_ref_vector& objectives, svector<bool> const& is_max,
app_ref_vector& objectives,
vector<inf_eps_rational<inf_rational> >& values) {
return mathsat_style_opt(s, objectives, is_max, values);
return mathsat_style_opt(s, objectives, values);
}
}