Test and fix for bug in PLResolution (reported by Huy Dinh)

Author: magicindian

ReadMe.txt

@@ -16,16 +16,17 @@ The official release can be found at http://aima.cs.berkeley.edu/java-overview.h
 The following people sent in excellent comments and bug reports.
  Thank you all
 
+Huy Dinh, for reporting a prticularly insidious bog in the Logic code
 
- Carl Anderson Senior Scientist, ArchimedesModel.com (suggested making heuristic values double instead of int. Excellent suggestion! Than You!)
+Carl Anderson Senior Scientist, ArchimedesModel.com (suggested making heuristic values double instead of int. Excellent suggestion! Thank You!)
 
 Don Cochrane from (?) University
 
 Mike Angelotti  from Miami University
 
 Chad Carff ,University of Western Florida .  EXCELLENT test cases . thank you .
 
-Dr .Eman El-Sheikh, Ph.D.,University of Western Florida
+Dr. Eman El-Sheikh, Ph.D.,University of Western Florida
 
 Ravindra Guravannavar, Aztec Software,Bangalore
 

src/aima/logic/propositional/algorithms/PLResolution.java

@@ -50,6 +50,8 @@ public boolean plResolution(KnowledgeBase kb, Sentence alpha) {
 				List<Sentence> pair = pairs.get(i);
 				// System.out.println("pair number" + i+" of "+pairs.size());
 				Set<Sentence> resolvents = plResolve(pair.get(0), pair.get(1));
+				resolvents = filterOutClausesWithTwoComplementaryLiterals(resolvents);
+
 				if (resolvents.contains(new Symbol("EMPTY_CLAUSE"))) {
 					return true;
 				}

src/aima/test/logictest/prop/algorithms/PLResolutionTest.java

@@ -7,6 +7,7 @@
 import java.util.Set;
 
 import junit.framework.TestCase;
+import aima.logic.propositional.algorithms.KnowledgeBase;
 import aima.logic.propositional.algorithms.PLResolution;
 import aima.logic.propositional.parsing.PEParser;
 import aima.logic.propositional.parsing.ast.Sentence;
@@ -95,8 +96,18 @@ public void testPLResolve5() {
 		assertEquals(false, b);
 	}
 
-	// public void testPLResolutionWithChadCarfBugReportData(){
-	// //commented out coz too slow..
+	public void testMultipleClauseResolution() {
+		// test (and fix) suggested by Huy Dinh. Thanks Huy!
+		PLResolution plr = new PLResolution();
+		KnowledgeBase kb = new KnowledgeBase();
+		String fact = "((B11 <=> (P12 OR P21)) AND (NOT B11))";
+		kb.tell(fact);
+		plr.plResolution(kb, "(B)");
+
+	}
+
+	// public void testPLResolutionWithChadCarfBugReportData() {
+	// commented out coz this needs a major fix wait for a rewrite
 	// KnowledgeBase kb = new KnowledgeBase();
 	// kb.tell("(B12 <=> (P11 OR (P13 OR (P22 OR P02))))");
 	// kb.tell("(B21 <=> (P20 OR (P22 OR (P31 OR P11))))");
@@ -106,7 +117,7 @@ public void testPLResolve5() {
 	// kb.tell("(NOT B12)");
 	// kb.tell("(B10)");
 	// kb.tell("(B01)");
-	// assertTrue(resolution.plResolution(kb.asSentence().toString(),"(P00)"));
+	// assertTrue(resolution.plResolution(kb.asSentence().toString(), "(P00)"));
 	// //assertFalse(kb.askWithDpll("(NOT P00)"));
 	//		
 	//