add option to "rotate" cores during core finding

enable to find multiple cores in a round and at the same time facilitate rotation around satisfiable subsets to explore neighborhoods for improved assignments.

src/opt/opt_cores.h

@@ -0,0 +1,71 @@
+/*++
+Copyright (c) 2022 Microsoft Corporation
+
+Module Name:
+
+    opt_cores.h
+
+Abstract:
+   
+    "walk" subsets of soft constraints to extract multiple cores and satisfying assignments.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2022-04-27
+
+--*/
+
+#pragma once
+#include "opt/opt_lns.h"
+
+namespace opt {
+
+
+    class cores {
+        ast_manager&     m;
+        solver&          s;
+        lns_context&     ctx;
+
+        random_gen               m_rand;
+        rational                 m_best_cost = rational::minus_one();
+        vector<weighted_core>    m_cores;
+        obj_map<expr, rational>  m_weight;
+
+        unsigned m_max_saturate_conflicts = 500;
+        unsigned m_max_conflicts          = 1000;
+        bool     m_hill_climb             = true;
+        unsigned m_max_num_cores          = UINT_MAX;
+        unsigned m_max_core_size          = 4;
+        bool     m_enable_core_rotate     = false;
+
+        struct scoped_update;
+
+        bool improve();
+        void rotate_rec(obj_hashtable<expr> const& mss, obj_map<expr, ptr_vector<expr>>& backbone2core, unsigned depth);
+        bool rotate(obj_hashtable<expr> const& mss, expr* excl, unsigned depth);
+        void saturate_core(expr_ref_vector& core);
+        void local_mss();
+        void hitting_set(obj_hashtable<expr>& hs);
+        rational core_weight(expr_ref_vector const& core) { return core_weight(core.size(), core.data()); }
+        rational core_weight(ptr_vector<expr> const& core) { return core_weight(core.size(), core.data()); }
+        rational core_weight(unsigned sz, expr* const* core);
+        lbool check_sat_hill_climb(expr_ref_vector const& _soft);
+
+        void add_core(expr_ref_vector const& core);
+
+        vector<weighted_core> const& disjoint_cores();
+
+        void rotate_cores();
+
+        vector<weighted_core> const& weighted_disjoint_cores();
+
+        expr_ref_vector unsat_core();
+
+    public:
+        cores(solver& s, lns_context& ctx);
+        
+        vector<weighted_core> const& operator()();
+
+        void updt_params(params_ref& p);
+    };
+};