Resolve issue 15

lib/grobner.gi

@@ -627,7 +627,7 @@ end);;
 ###
 
 GBNP.ReducePol2:=function(arg) 
-local i,j,jl,h,ind,lts,new,lans,newind,temp,G,GLOT;
+local i,j,jl,h,ind,lts,new,lans,newind,temp,G,GLOT,done,one;
     G:=arg[1]; 
     if Length(arg)>=2 then
     	GLOT:=arg[2]; 
@@ -650,13 +650,38 @@ local i,j,jl,h,ind,lts,new,lans,newind,temp,G,GLOT;
     	SortParallel(lts,G,LtNP);
     	GBNP.SortParallelLOT(temp,GLOT,LtNP);
     else
-    	for i in [1..Length(G)] do
-		G[i]:=GBNP.ReduceCancellation(G[i]);
-	od;
-        lts:=LMonsNP(G);
-    	SortParallel(lts,G,LtNP);
+        done := false; 
+        while not done do
+    		for i in [1..Length(G)] do
+	    		G[i]:=GBNP.ReduceCancellation(G[i]);
+		od;
+        	lts:=LMonsNP(G);
+    		SortParallel(lts,G,LtNP);
+                done := true; 
+                for i in Reversed( [1..Length(lts)-1] ) do 
+                     if ( lts[i] = lts[i+1] ) then
+                         done := false; 
+## Print( "G[i],G[i+1] = ", G[i], G[i+1], "\n" ); 
+                         one:=One(G[i][2][1]);
+                         G[i+1] := CleanNP(AddNP(G[i+1],G[i],one,-one));
+## Print( "new G[i+1] = ", G[i+1], "\n" );
+                     fi;
+                od;
+                if not done then 
+                    ## need to resort G 
+                    lts:=LMonsNP(G); 
+    	            SortParallel(lts,G,LtNP);
+## Print( "resorted lts and G:\n", lts, "\n", G, "\n" ); 
+                fi; 
+        od; 
+
+## Print( "after SortParallel G and lts =:\n", G, "\n", lts, "\n" ); 
+
 	GLOT:=GBNP.CreateOccurTreePTSLR(lts,GBNP.CalculatePGlts(lts),true);
     fi;
+
+## Print( "initial GLOT:\n", GLOT, "\n" ); 
+
     lans:=Length(lts);
     ind:=[1..lans];
 
@@ -665,6 +690,9 @@ local i,j,jl,h,ind,lts,new,lans,newind,temp,G,GLOT;
         RemoveSet(ind,i);
         j:=i+1;
 	while j <= lans do 
+
+## Print( "[i,j] = ", [i,j], "\n" ); 
+
 	    if #IsSubsetBlist(Gset[j],Gset[i]) and 
 	    		GBNP.Occur(G[i][1][1],G[j][1][1]) <> 0 
 		# XXX can this occur be removed
@@ -890,14 +918,15 @@ Grobner,function(arg) local tt,todo,G, funcs,KI,loop, withpair;
 # - Compute internal NormalForm 
 
      Info(InfoGBNP,1,"number of entered polynomials is ",Length(KI));
-
      if (withpair) then
          # no cleaning should be needed when continuing
          G:= ShallowCopy(KI);
      else
          G:= GBNP.ReducePol(KI);
      fi;
-
+
+## Print( "here is the resulting G\n", G, "\n" ); 
+
      # only call GBNP.CalculatePG after reduction
      funcs.pg:=GBNP.CalculatePG(G);
 
@@ -1023,7 +1052,6 @@ SGrobner,function(arg) local tt,todo,G,GLOT,funcs,KI,loop,withpair;
     else
       KI:=arg[1];
     fi;
-
     tt:=Runtime(); 
 
     if Length(arg)>=2 and IsInt(arg[Length(arg)]) then
@@ -1308,11 +1336,17 @@ end);;
 
 GBNP.StrongNormalForm2TS:=function(G,j,GLOT) 
     local g,h,il,i1,l,dr,ga,tt,lth,iid;
+
+## Print( "in StrongNormalForm2TS G[j] = ", G[j], "\n" ); 
+
     h:=StructuralCopy(G[j]); 
     iid := 1; 
     while iid <= Length(h[1]) do 
       lth:=h[1][iid];  
       il:=GBNP.LookUpOccurTreeAllLstPTSLR(lth,GLOT,true); 
+
+## Print( "il = ", il, "\n" ); 
+
       il:=Filtered(il,x->x[1]<>j);
       while il<>[] do 
 	   i1:=il[1];

lib/occurtree.gi

@@ -121,7 +121,7 @@ end;
 ###
 
 GBNP.CreateOccurTreePTSLR:=function(L,pg,left)
-        if (pg <> GBNP.GetOptions().pg) then
+        if (pg <> GBNP.GetOptions().pg) then 
 		Info(InfoGBNP,2,"Warning: CreateOccurTreePTSLR: pg argument (",pg,") is not the same as pg option (",GBNP.GetOptions().pg,")\n");
 	fi;
 

tst/issue15.g

@@ -0,0 +1,10 @@
+LoadPackage("gbnp");
+SetInfoLevel( InfoGBNP, 2 ); 
+A:=FreeAssociativeAlgebraWithOne(Rationals,"a","b");
+a:=A.1;
+b:=A.2;
+rels := [ a^3, a^2*b, a*b^2+a^2, b*a^2, a^3+b^2+b*a, a*b^2+a*b*a, 
+          b*a*b+b*a^2, b^2*a+b*a^2, b^3+b*a^2, a^2*b*a, a*b*a^2, b*a^2*b ];
+relsnp := List( rels, x-> GP2NP(x) );
+grobnp := Grobner(relsnp); 
+grob := List( grobnp, p -> NP2GP(p,A) ); 

tst/issue15.tst

@@ -0,0 +1,23 @@
+gap> START_TEST("GBNP issue 15");
+gap> 
+gap> LoadPackage("gbnp");;
+gap> 
+gap> A:=FreeAssociativeAlgebraWithOne(Rationals,"a","b");;
+gap> a:=A.1;;
+gap> b:=A.2;;
+gap> rels := [ a^3, a^2*b, a*b^2+a^2, b*a^2, a^3+b^2+b*a, 
+>              a*b^2+a*b*a, b*a*b+b*a^2, b^2*a+b*a^2, b^3+b*a^2, 
+>              a^2*b*a, a*b*a^2, b*a^2*b ];;
+gap> Display(rels);
+[ (1)*a^3, (1)*a^2*b, (1)*a^2+(1)*a*b^2, (1)*b*a^2, (1)*b*a+(1)*b^2+(1)*a^3, 
+  (1)*a*b*a+(1)*a*b^2, (1)*b*a^2+(1)*b*a*b, (1)*b*a^2+(1)*b^2*a, 
+  (1)*b*a^2+(1)*b^3, (1)*a^2*b*a, (1)*a*b*a^2, (1)*b*a^2*b ]
+gap> relsnp := List( rels, x-> GP2NP(x) );;
+gap> grobnp := Grobner(relsnp);;
+gap> grob := List( grobnp, p -> NP2GP(p,A) );; 
+gap> Display(grob); 
+[ (1)*b^2+(1)*b*a, (1)*a^3, (1)*a^2*b, (1)*a*b*a+(-1)*a^2, (1)*b*a^2, 
+  (1)*b*a*b+(1)*b*a^2 ]
+gap> 
+gap> STOP_TEST("GBNP issue 15",10000);
+