some fixes in branching

Signed-off-by: Lev Nachmanson <levnach@hotmail.com>

src/math/lp/int_branch.cpp

@@ -1,119 +1,118 @@
 /*++
-Copyright (c) 2020 Microsoft Corporation
+  Copyright (c) 2020 Microsoft Corporation
 
-Module Name:
+  Module Name:
 
-    int_branch.cpp
+  int_branch.cpp
 
-Abstract:
+  Abstract:
 
-    Branch heuristic
+  Branch heuristic
 
-Author:
-    Lev Nachmanson (levnach)
-    Nikolaj Bjorner (nbjorner)
+  Author:
+  Lev Nachmanson (levnach)
+  Nikolaj Bjorner (nbjorner)
 
-Revision History:
---*/
+  Revision History:
+  --*/
 
 #include "math/lp/int_solver.h"
 #include "math/lp/lar_solver.h"
 #include "math/lp/int_branch.h"
 
 namespace lp {
 
-    int_branch::int_branch(int_solver& lia):lia(lia), lra(lia.lra) {}
-
-    lia_move int_branch::operator()() {
-        int j = find_any_inf_int_column_basis_first();
-        return j == -1? lia_move::sat : create_branch_on_column(j);        
-    }
-
-    int int_branch::find_any_inf_int_column_basis_first() {
-        int j = find_inf_int_base_column();
-        return j != -1 ? j : find_inf_int_nbasis_column();
-    }
+int_branch::int_branch(int_solver& lia):lia(lia), lra(lia.lra) {}
 
+lia_move int_branch::operator()() {
+    int j = find_any_inf_int_column_basis_first();
+    return j == -1? lia_move::sat : create_branch_on_column(j);        
+}
 
-    lia_move int_branch::create_branch_on_column(int j) {
-        TRACE("check_main_int", tout << "branching" << std::endl;);
-        lp_assert(lia.m_t.is_empty());
-        lp_assert(j != -1);
-        lia.m_t.add_monomial(mpq(1), lra.adjust_column_index_to_term_index(j));
-        if (lia.is_free(j)) {
-            lia.m_upper = lia.random() % 2;
-            lia.m_k = mpq(0);
-        }
-        else {
-            lia.m_upper = lia.random() % 2;
-            lia.m_k = lia.m_upper? floor(lia.get_value(j)) : ceil(lia.get_value(j));        
-        }
-
-        TRACE("int_solver",
-              lia.display_column(tout << "branching v" << j << " = " << lia.get_value(j) << "\n", j);
-              tout << "k = " << lia.m_k << std::endl;);
-        return lia_move::branch;        
-    }
+int int_branch::find_any_inf_int_column_basis_first() {
+    int j = find_inf_int_base_column();
+    return j != -1 ? j : find_inf_int_nbasis_column();
+}
 
-    int int_branch::find_inf_int_base_column() {
-        unsigned inf_int_count = 0;
-        int j = find_inf_int_boxed_base_column_with_smallest_range(inf_int_count);
-        if (j != -1) {
-            return j;
-        }
-        if (inf_int_count == 0)
-            return -1;
-        unsigned k = lia.random() % inf_int_count;
-        return get_kth_inf_int(k);
+lia_move int_branch::create_branch_on_column(int j) {
+    TRACE("check_main_int", tout << "branching" << std::endl;);
+    lp_assert(lia.m_t.is_empty());
+    lp_assert(j != -1);
+    lia.m_t.add_monomial(mpq(1), lra.adjust_column_index_to_term_index(j));
+    if (lia.is_free(j)) {
+        lia.m_upper = lia.random() % 2;
+        lia.m_k = mpq(0);
     }
-
-    int int_branch::get_kth_inf_int(unsigned k) const {
-        for (unsigned j : lra.r_basis()) 
-            if (lia.column_is_int_inf(j) && k-- == 0)
-                return j;
-        lp_assert(false);
-        return -1;
+    else {
+        lia.m_upper = lia.random() % 2;
+        lia.m_k = lia.m_upper? floor(lia.get_value(j)) : ceil(lia.get_value(j));        
     }
-
-    int int_branch::find_inf_int_nbasis_column() const {
 
-        for (unsigned j : lra.r_nbasis())
-            if (lia.column_is_int_inf(j)) {
-                return j;    
+    TRACE("int_solver",
+          lia.display_column(tout << "branching v" << j << " = " << lia.get_value(j) << "\n", j);
+          tout << "k = " << lia.m_k << std::endl;);
+    return lia_move::branch;        
+}
+
+
+int int_branch::find_inf_int_nbasis_column() const {
+    unsigned n = 0;
+    int r = -1;
+    for (unsigned j : lra.r_nbasis()) {
+        SASSERT(!lia.column_is_int_inf(j) || !lia.is_fixed(j));
+        if (lia.column_is_int_inf(j)) {
+            if (n == 0) {
+                r = j;
+                n = 1;                    
+            } else if (lia.random() % (++n) == 0) {
+                r = j;
             }
-        return -1; 
+        }
     }
+    return r; 
+}
 
-    int int_branch::find_inf_int_boxed_base_column_with_smallest_range(unsigned & inf_int_count) {
-        inf_int_count = 0;
-        int result = -1;
-        mpq range;
-        mpq new_range;
-        mpq small_range_thresold(1024);
-        unsigned n = 0;
-        lar_core_solver & lcs = lra.m_mpq_lar_core_solver;
-
-        for (unsigned j : lra.r_basis()) {
-            if (!lia.column_is_int_inf(j))
-                continue;
-            inf_int_count++;
-            if (!lia.is_boxed(j))
+int int_branch::find_inf_int_base_column() {
+    int result = -1;
+    mpq range;
+    mpq new_range;
+    mpq small_range_thresold(1024);
+    unsigned n = 0;
+    lar_core_solver & lcs = lra.m_mpq_lar_core_solver;
+    bool small = false;
+    for (unsigned j : lra.r_basis()) {
+        SASSERT(!lia.column_is_int_inf(j) || !lia.is_fixed(j));
+        if (!lia.column_is_int_inf(j))
+            continue;
+        bool boxed = lia.is_boxed(j);
+        if (small) {
+            if (!boxed)
                 continue;
-            lp_assert(!lia.is_fixed(j));
             new_range  = lcs.m_r_upper_bounds()[j].x - lcs.m_r_lower_bounds()[j].x;
-            if (new_range > small_range_thresold) 
-                continue;
-            if (result == -1 || new_range < range) {
-                result = j;
-                range  = new_range;
-                n      = 1;
-            }
-            else if (new_range == range && lia.random() % (++n) == 0) {
-                lp_assert(n > 1);
-                result = j;
+            if (new_range <= small_range_thresold) {
+                if (new_range < range) {
+                    n = 1;
+                    result = j;
+                    range = new_range;
+                } else if (new_range == range && lia.random() % (++n) == 0) {
+                    result = j;                    
+                }
             }
+        } else if (boxed &&
+                   (new_range = lcs.m_r_upper_bounds()[j].x - lcs.m_r_lower_bounds()[j].x)
+                   <= small_range_thresold) {
+            small = true;
+            result = j;
+            range = new_range;
+            n = 1;
+        } else if (result == -1) {
+            result = j;
+            n      = 1;
+        } else if (lia.random() % (++n) == 0) {
+            result = j;
         }
-        return result;    
     }
+    return result;    
+}
 
 }

src/math/lp/int_branch.h

@@ -29,10 +29,8 @@ namespace lp {
         class lar_solver& lra;
         lia_move create_branch_on_column(int j);
         int find_inf_int_base_column();
-        int get_kth_inf_int(unsigned k) const;
         int find_inf_int_nbasis_column() const;
         int find_any_inf_int_column_basis_first();
-        int find_inf_int_boxed_base_column_with_smallest_range(unsigned & inf_int_count);
 
     public:
         int_branch(int_solver& lia);