Index: matrix.cpp
===================================================================
RCS file: /home/cvs/GiNaC/ginac/matrix.cpp,v
retrieving revision 1.111
diff -u -r1.111 matrix.cpp
--- matrix.cpp	31 Jan 2007 22:29:20 -0000	1.111
+++ matrix.cpp	18 Feb 2008 22:16:44 -0000
@@ -1414,7 +1414,11 @@
 	
 	unsigned r0 = 0;
 	for (unsigned c0=0; c0<n && r0<m-1; ++c0) {
-		int indx = tmp_n.pivot(r0, c0, true);
+		// When trying to find a pivot, we need to try a bit harder than .expand() below.
+		matrix pivot_col(m-r0,1);
+		for (unsigned r1=r0; r1<m; ++r1)
+			pivot_col(r1-r0,0) = tmp_n(r1,c0).subs(srl, subs_options::no_pattern).expand().to_rational(srl);
+		int indx = pivot_col.pivot(0, 0, true);
 		if (indx==-1) {
 			sign = 0;
 			if (det)
@@ -1423,9 +1427,13 @@
 		if (indx>=0) {
 			if (indx>0) {
 				sign = -sign;
-				// tmp_n's rows r0 and indx were swapped, do the same in tmp_d:
-				for (unsigned c=c0; c<n; ++c)
+				// Swap rows in tmp_n and tmp_d, remembering that indx is relative
+				// to pivot_col.
+				indx += r0;
+				for (unsigned c=c0; c<n; ++c) {
+					tmp_n.m[n*indx+c].swap(tmp_n.m[n*r0+c]);
 					tmp_d.m[n*indx+c].swap(tmp_d.m[n*r0+c]);
+				}
 			}
 			for (unsigned r2=r0+1; r2<m; ++r2) {
 				for (unsigned c=c0+1; c<n; ++c) {