[Lemon-commits] Balazs Dezso: Fix critical bug in preflow (#372)

[Lemon HG]

details:   http://lemon.cs.elte.hu/hg/lemon/rev/bb70ad62c95f
changeset: 982:bb70ad62c95f
user:      Balazs Dezso <deba [at] inf.elte.hu>
date:      Thu Jun 24 09:27:53 2010 +0200
description:
	Fix critical bug in preflow (#372)

	The wrong transition between the bound decrease and highest active
	heuristics caused the bug. The last node chosen in bound decrease
	mode is used in the first iteration in highest active mode.

diffstat:

 lemon/preflow.h |  44 ++++++++++++++++++++++++--------------------
 1 files changed, 24 insertions(+), 20 deletions(-)

diffs (75 lines):

diff --git a/lemon/preflow.h b/lemon/preflow.h
--- a/lemon/preflow.h
+++ b/lemon/preflow.h
@@ -558,12 +558,18 @@
     void startFirstPhase() {
       _phase = true;
 
-      Node n = _level->highestActive();
-      int level = _level->highestActiveLevel();
-      while (n != INVALID) {
+      while (true) {
         int num = _node_num;
 
-        while (num > 0 && n != INVALID) {
+        Node n = INVALID;
+        int level = -1;
+
+        while (num > 0) {
+          n = _level->highestActive();
+          if (n == INVALID) goto first_phase_done;
+          level = _level->highestActiveLevel();
+          --num;
+          
           Value excess = (*_excess)[n];
           int new_level = _level->maxLevel();
 
@@ -629,14 +635,22 @@
           } else {
             _level->deactivate(n);
           }
-
-          n = _level->highestActive();
-          level = _level->highestActiveLevel();
-          --num;
         }
 
         num = _node_num * 20;
-        while (num > 0 && n != INVALID) {
+        while (num > 0) {
+          while (level >= 0 && _level->activeFree(level)) {
+            --level;
+          }
+          if (level == -1) {
+            n = _level->highestActive();
+            level = _level->highestActiveLevel();
+            if (n == INVALID) goto first_phase_done;
+          } else {
+            n = _level->activeOn(level);
+          }
+          --num;
+
           Value excess = (*_excess)[n];
           int new_level = _level->maxLevel();
 
@@ -702,19 +716,9 @@
           } else {
             _level->deactivate(n);
           }
-
-          while (level >= 0 && _level->activeFree(level)) {
-            --level;
-          }
-          if (level == -1) {
-            n = _level->highestActive();
-            level = _level->highestActiveLevel();
-          } else {
-            n = _level->activeOn(level);
-          }
-          --num;
         }
       }
+    first_phase_done:;
     }
 
     /// \brief Starts the second phase of the preflow algorithm.