review comments by Elffers

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/ast/rewriter/pb2bv_rewriter.cpp

@@ -926,6 +926,8 @@ struct pb2bv_rewriter::imp {
 
         void set_cardinality_encoding(sorting_network_encoding enc) { m_sort.cfg().m_encoding = enc; }
 
+        void set_min_arity(unsigned ma) { m_min_arity = ma; }
+
     };
 
     struct card2bv_rewriter_cfg : public default_rewriter_cfg {
@@ -940,6 +942,7 @@ struct pb2bv_rewriter::imp {
         void keep_cardinality_constraints(bool f) { m_r.keep_cardinality_constraints(f); }
         void set_pb_solver(symbol const& s) { m_r.set_pb_solver(s); }
         void set_cardinality_encoding(sorting_network_encoding enc) { m_r.set_cardinality_encoding(enc); }
+        void set_min_arity(unsigned ma) { m_r.set_min_arity(ma); }
 
     };
     
@@ -952,6 +955,7 @@ struct pb2bv_rewriter::imp {
         void keep_cardinality_constraints(bool f) { m_cfg.keep_cardinality_constraints(f); }
         void set_pb_solver(symbol const& s) { m_cfg.set_pb_solver(s); }
         void set_cardinality_encoding(sorting_network_encoding e) { m_cfg.set_cardinality_encoding(e); }
+        void set_min_arity(unsigned ma) { m_cfg.set_min_arity(ma); }
         void rewrite(bool full, expr* e, expr_ref& r, proof_ref& p) {
             expr_ref ee(e, m());
             if (m_cfg.m_r.mk_app(full, e, r)) {
@@ -982,6 +986,15 @@ struct pb2bv_rewriter::imp {
         return gparams::get_module("sat").get_sym("pb.solver", symbol("solver"));
     }
 
+    unsigned min_arity() const {
+        params_ref const& p = m_params;
+        unsigned r = p.get_uint("sat.pb.min_arity", UINT_MAX);
+        if (r != UINT_MAX) return r;
+        r = p.get_uint("pb.min_arity", UINT_MAX);
+        if (r != UINT_MAX) return r;
+        return gparams::get_module("sat").get_uint("pb.min_arity", 9);
+    }
+
     sorting_network_encoding cardinality_encoding() const {
         symbol enc = m_params.get_sym("cardinality.encoding", symbol());
         if (enc == symbol()) {
@@ -1011,6 +1024,7 @@ struct pb2bv_rewriter::imp {
         m_rw.keep_cardinality_constraints(keep_cardinality());
         m_rw.set_pb_solver(pb_solver());
         m_rw.set_cardinality_encoding(cardinality_encoding());
+        m_rw.set_min_arity(min_arity());
     }
 
     void collect_param_descrs(param_descrs& r) const {

src/sat/ba_solver.cpp

@@ -1400,6 +1400,12 @@ namespace sat {
             unsigned ci = ineq.coeff(i); 
             unsigned q = ci % c;
             if (q != 0 && !is_false(ineq.lit(i))) {
+#if 1
+                // code review by Elffers:
+                ineq.weaken(i);
+                --i;
+                --sz;                
+#else
                 if (q == ci) {
                     ineq.weaken(i);
                     --i;
@@ -1409,6 +1415,7 @@ namespace sat {
                     ineq.m_wlits[i].first -= q;
                     ineq.m_k -= q;
                 }
+#endif
             }
         }
         ineq.divide(c);

src/sat/sat_params.pyg

@@ -48,6 +48,7 @@ def_module_params('sat',
                           ('drat.check_sat', BOOL, False, 'build up internal trace, check satisfying model'),
                           ('cardinality.solver', BOOL, True, 'use cardinality solver'),
                           ('pb.solver', SYMBOL, 'solver', 'method for handling Pseudo-Boolean constraints: circuit (arithmetical circuit), sorting (sorting circuit), totalizer (use totalizer encoding), binary_merge, segmented, solver (use native solver)'),
+                          ('pb.min_arity', UINT, 9, 'minimal arity to compile pb/cardinality constraints to CNF'),
                           ('xor.solver', BOOL, False, 'use xor solver'),                        
                           ('cardinality.encoding', SYMBOL, 'grouped', 'encoding used for at-most-k constraints: grouped, bimander, ordered, unate, circuit'),
                           ('pb.resolve', SYMBOL, 'cardinality', 'resolution strategy for boolean algebra solver: cardinality, rounding'),

src/sat/sat_solver.cpp

@@ -3161,12 +3161,42 @@ namespace sat {
         m_activity_inc = 128;
         svector<bool_var> vars;
         for (bool_var v = num_vars(); v-- > 0; ) {
-            vars.push_back(v);
+            if (!was_eliminated(v) && value(v) == l_undef) {            
+                vars.push_back(v);
+            }
         }
+#if 1
+        // 
+        //   exp(logits[i]) / sum(exp(logits)) 
+        // = 
+        //   exp(log(exp(logits[i]) / sum(exp(logits)))) 
+        // = 
+        //   exp(log(exp(logits[i])) - log(sum(exp(logits)))) 
+        // =
+        //   exp(logits[i] - lse)
+        svector<float> logits(vars.size(), 0.0);
+        float itau = 4.0;
+        float lse = 0;
+        float mid = m_rand.max_value()/2;
+        float max = 0;
+        for (float& f : logits) {
+            f = itau * (m_rand() - mid)/mid;
+            if (f > max) max = f;
+        }
+        for (float f : logits) {
+            lse += log(f - max);
+        }
+        lse = max + exp(lse);
+
+        for (unsigned i = 0; i < vars.size(); ++i) {
+            update_activity(vars[i], exp(logits[i] - lse));
+        }
+#else
         shuffle(vars.size(), vars.c_ptr(), m_rand);
         for (bool_var v : vars) {
-            update_activity(v, m_rand(10));
+            update_activity(v, m_rand(10)/10.0);
         }
+#endif
         m_reorder_inc += m_config.m_reorder_base;
         m_reorder_lim += m_reorder_inc;
     }