From d2de9f5307c47adb2df13359002d987653c38a6a Mon Sep 17 00:00:00 2001
From: Chris Dams <Chris.Dams@mi.infn.it>
Date: Wed, 16 May 2007 23:21:09 +0000
Subject: [PATCH] Patch by Stefan Weinzierl that fixes a bug in series
 expansion.

---
 check/exam_pseries.cpp | 13 +++++++++++
 ginac/pseries.cpp      | 51 +++++++++++++++++++++++++++++++++++++++---
 2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/check/exam_pseries.cpp b/check/exam_pseries.cpp
index b0ccac3e..1c8acd93 100644
--- a/check/exam_pseries.cpp
+++ b/check/exam_pseries.cpp
@@ -348,6 +348,18 @@ static unsigned exam_series12()
 	return result;
 }
 
+// Test of the patch of Stefan Weinzierl that prevents an infinite loop if
+// a factor in a product is a complicated way of writing zero.
+static unsigned exam_series13()
+{
+	unsigned result = 0;
+
+	ex e = pow(2,x)*( 1/x*(-(1+x)/(1-x)) + (1+x)/x/(1-x));
+	ex d = Order(x);
+	result += check_series(e,0,d,1);
+
+	return result;
+}
 
 unsigned exam_pseries()
 {
@@ -368,6 +380,7 @@ unsigned exam_pseries()
 	result += exam_series10();  cout << '.' << flush;
 	result += exam_series11();  cout << '.' << flush;
 	result += exam_series12();  cout << '.' << flush;
+	result += exam_series13();  cout << '.' << flush;
 	
 	if (!result) {
 		cout << " passed " << endl;
diff --git a/ginac/pseries.cpp b/ginac/pseries.cpp
index ec8e8c65..0da6ae8d 100644
--- a/ginac/pseries.cpp
+++ b/ginac/pseries.cpp
@@ -892,10 +892,13 @@ ex mul::series(const relational & r, int order, unsigned options) const
 		
 	// holds ldegrees of the series of individual factors
 	std::vector<int> ldegrees;
+	std::vector<bool> ldegree_redo;
 
 	// find minimal degrees
 	const epvector::const_iterator itbeg = seq.begin();
 	const epvector::const_iterator itend = seq.end();
+	// first round: obtain a bound up to which minimal degrees have to be
+	// considered
 	for (epvector::const_iterator it=itbeg; it!=itend; ++it) {
 
 		ex expon = it->coeff;
@@ -909,19 +912,61 @@ ex mul::series(const relational & r, int order, unsigned options) const
 		}
 
 		int real_ldegree = 0;
+		bool flag_redo = false;
 		try {
 			real_ldegree = buf.expand().ldegree(sym-r.rhs());
 		} catch (std::runtime_error) {}
 
 		if (real_ldegree == 0) {
+			if ( factor < 0 ) {
+				// This case must terminate, otherwise we would have division by
+				// zero.
+				int orderloop = 0;
+				do {
+					orderloop++;
+					real_ldegree = buf.series(r, orderloop, options).ldegree(sym);
+				} while (real_ldegree == orderloop);
+			} else {
+				// Here it is possible that buf does not have a ldegree, therefore
+				// check only if ldegree is negative, otherwise reconsider the case
+				// in the second round.
+				real_ldegree = buf.series(r, 0, options).ldegree(sym);
+				if (real_ldegree == 0)
+					flag_redo = true;
+			}
+		}
+
+		ldegrees.push_back(factor * real_ldegree);
+		ldegree_redo.push_back(flag_redo);
+	}
+
+	int degbound = order-std::accumulate(ldegrees.begin(), ldegrees.end(), 0);
+	// Second round: determine the remaining positive ldegrees by the series
+	// method.
+	// here we can ignore ldegrees larger than degbound
+	size_t j = 0;
+	for (epvector::const_iterator it=itbeg; it!=itend; ++it) {
+		if ( ldegree_redo[j] ) {
+			ex expon = it->coeff;
+			int factor = 1;
+			ex buf;
+			if (expon.info(info_flags::integer)) {
+				buf = it->rest;
+				factor = ex_to<numeric>(expon).to_int();
+			} else {
+				buf = recombine_pair_to_ex(*it);
+			}
+			int real_ldegree = 0;
 			int orderloop = 0;
 			do {
 				orderloop++;
 				real_ldegree = buf.series(r, orderloop, options).ldegree(sym);
-			} while (real_ldegree == orderloop);
+			} while ((real_ldegree == orderloop)
+					&& ( factor*real_ldegree < degbound));
+			ldegrees[j] = factor * real_ldegree;
+			degbound -= factor * real_ldegree;
 		}
-
-		ldegrees.push_back(factor * real_ldegree);
+		j++;
 	}
 
 	int degsum = std::accumulate(ldegrees.begin(), ldegrees.end(), 0);
-- 
2.44.0