From: Chris Dams <Chris.Dams@mi.infn.it>
Date: Wed, 22 Nov 2006 22:16:20 +0000 (+0000)
Subject: Backport change in reposition_dummy_indices to 1.3.
X-Git-Tag: release_1-3-6~9
X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?a=commitdiff_plain;h=4f5d44895414656822598aca037d196a2fc8d974;p=ginac.git

Backport change in reposition_dummy_indices to 1.3.
---

diff --git a/check/exam_paranoia.cpp b/check/exam_paranoia.cpp
index 7c82e486..0ab64910 100644
--- a/check/exam_paranoia.cpp
+++ b/check/exam_paranoia.cpp
@@ -437,6 +437,33 @@ static unsigned exam_paranoia16()
 	return result;
 }
 
+// Bug in reposition_dummy_indices() could result in correct expression
+// turned into one with inconsistent indices. Fixed on Aug 29, 2006
+static unsigned exam_paranoia17()
+{
+	varidx mu1(symbol("mu1"), 4);
+	varidx mu2(symbol("mu2"), 4);
+	varidx mu3(symbol("mu3"), 4);
+	varidx mu4(symbol("mu4"), 4);
+	varidx mu5(symbol("mu5"), 4);
+	varidx mu6(symbol("mu6"), 4);
+
+	exvector ev2;
+	ev2.push_back(mu3.toggle_variance());
+	ev2.push_back(mu6);
+	ev2.push_back(mu5.toggle_variance());
+	ev2.push_back(mu6.toggle_variance());
+	ev2.push_back(mu5);
+	ev2.push_back(mu3); 
+	// notice: all indices are contracted ...
+
+	ex test_cycl = indexed(symbol("A"), sy_cycl(), ev2);
+	test_cycl = test_cycl.simplify_indexed();
+	// ... so there should be zero free indices in the end.
+	return test_cycl.get_free_indices().size();
+}
+
+
 unsigned exam_paranoia()
 {
 	unsigned result = 0;
@@ -460,6 +487,7 @@ unsigned exam_paranoia()
 	result += exam_paranoia14();  cout << '.' << flush;
 	result += exam_paranoia15();  cout << '.' << flush;
 	result += exam_paranoia16();  cout << '.' << flush;
+	result += exam_paranoia17();  cout << '.' << flush;
 	
 	if (!result) {
 		cout << " passed " << endl;
diff --git a/ginac/indexed.cpp b/ginac/indexed.cpp
index 05c3b90a..2de726bf 100644
--- a/ginac/indexed.cpp
+++ b/ginac/indexed.cpp
@@ -632,10 +632,60 @@ bool reposition_dummy_indices(ex & e, exvector & variant_dummy_indices, exvector
 {
 	bool something_changed = false;
 
+	// Find dummy symbols that occur twice in the same indexed object.
+	exvector local_var_dummies;
+	local_var_dummies.reserve(e.nops()/2);
+	for (size_t i=1; i<e.nops(); ++i) {
+		if (!is_a<varidx>(e.op(i)))
+			continue;
+		for (size_t j=i+1; j<e.nops(); ++j) {
+			if (is_dummy_pair(e.op(i), e.op(j))) {
+				local_var_dummies.push_back(e.op(i));
+				for (exvector::iterator k = variant_dummy_indices.begin();
+						k!=variant_dummy_indices.end(); ++k) {
+					if (e.op(i).op(0) == k->op(0)) {
+						variant_dummy_indices.erase(k);
+						break;
+					}
+				}
+				break;
+			}
+		}
+	}
+
+	// In the case where a dummy symbol occurs twice in the same indexed object
+	// we try all posibilities of raising/lowering and keep the least one in
+	// the sense of ex_is_less.
+	ex optimal_e = e;
+	size_t numpossibs = 1 << local_var_dummies.size();
+	for (size_t i=0; i<numpossibs; ++i) {
+		ex try_e = e;
+		for (size_t j=0; j<local_var_dummies.size(); ++j) {
+			exmap m;
+			if (1<<j & i) {
+				ex curr_idx = local_var_dummies[j];
+				ex curr_toggle = ex_to<varidx>(curr_idx).toggle_variance();
+				m[curr_idx] = curr_toggle;
+				m[curr_toggle] = curr_idx;
+			}
+			try_e = e.subs(m, subs_options::no_pattern);
+		}
+		if(ex_is_less()(try_e, optimal_e))
+		{	optimal_e = try_e;
+			something_changed = true;
+		}
+	}
+	e = optimal_e;
+
+	if (!is_a<indexed>(e))
+		return true;
+
+	exvector seq = ex_to<indexed>(e).seq;
+
 	// If a dummy index is encountered for the first time in the
 	// product, pull it up, otherwise, pull it down
-	exvector::const_iterator it2, it2start, it2end;
-	for (it2start = ex_to<indexed>(e).seq.begin(), it2end = ex_to<indexed>(e).seq.end(), it2 = it2start + 1; it2 != it2end; ++it2) {
+	for (exvector::iterator it2 = seq.begin()+1, it2end = seq.end();
+			it2 != it2end; ++it2) {
 		if (!is_exactly_a<varidx>(*it2))
 			continue;
 
@@ -643,14 +693,20 @@ bool reposition_dummy_indices(ex & e, exvector & variant_dummy_indices, exvector
 		for (vit = variant_dummy_indices.begin(), vitend = variant_dummy_indices.end(); vit != vitend; ++vit) {
 			if (it2->op(0).is_equal(vit->op(0))) {
 				if (ex_to<varidx>(*it2).is_covariant()) {
-					e = e.subs(lst(
-						*it2 == ex_to<varidx>(*it2).toggle_variance(),
-						ex_to<varidx>(*it2).toggle_variance() == *it2
-					), subs_options::no_pattern);
+					/*
+					 * N.B. we don't want to use
+					 *
+					 *  e = e.subs(lst(
+					 *  *it2 == ex_to<varidx>(*it2).toggle_variance(),
+					 *  ex_to<varidx>(*it2).toggle_variance() == *it2
+					 *  ), subs_options::no_pattern);
+					 *
+					 * since this can trigger non-trivial repositioning of indices,
+					 * e.g. due to non-trivial symmetry properties of e, thus
+					 * invalidating iterators
+					 */
+					*it2 = ex_to<varidx>(*it2).toggle_variance();
 					something_changed = true;
-					it2 = ex_to<indexed>(e).seq.begin() + (it2 - it2start);
-					it2start = ex_to<indexed>(e).seq.begin();
-					it2end = ex_to<indexed>(e).seq.end();
 				}
 				moved_indices.push_back(*vit);
 				variant_dummy_indices.erase(vit);
@@ -661,11 +717,8 @@ bool reposition_dummy_indices(ex & e, exvector & variant_dummy_indices, exvector
 		for (vit = moved_indices.begin(), vitend = moved_indices.end(); vit != vitend; ++vit) {
 			if (it2->op(0).is_equal(vit->op(0))) {
 				if (ex_to<varidx>(*it2).is_contravariant()) {
-					e = e.subs(*it2 == ex_to<varidx>(*it2).toggle_variance(), subs_options::no_pattern);
+					*it2 = ex_to<varidx>(*it2).toggle_variance();
 					something_changed = true;
-					it2 = ex_to<indexed>(e).seq.begin() + (it2 - it2start);
-					it2start = ex_to<indexed>(e).seq.begin();
-					it2end = ex_to<indexed>(e).seq.end();
 				}
 				goto next_index;
 			}
@@ -674,6 +727,9 @@ bool reposition_dummy_indices(ex & e, exvector & variant_dummy_indices, exvector
 next_index: ;
 	}
 
+	if (something_changed)
+		e = ex_to<indexed>(e).thiscontainer(seq);
+
 	return something_changed;
 }