From 7e64f78f65db6681e6f71b80fa84c57bbce8200f Mon Sep 17 00:00:00 2001
From: Chen-Pang He <jdh8@ms63.hinet.net>
Date: Sat, 22 Sep 2012 22:06:22 +0800
Subject: [PATCH] Avoid inefficient 2x2 LU

---
 unsupported/Eigen/src/MatrixFunctions/MatrixPower.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/unsupported/Eigen/src/MatrixFunctions/MatrixPower.h b/unsupported/Eigen/src/MatrixFunctions/MatrixPower.h
index 2ed319641..08affb2b5 100644
--- a/unsupported/Eigen/src/MatrixFunctions/MatrixPower.h
+++ b/unsupported/Eigen/src/MatrixFunctions/MatrixPower.h
@@ -226,7 +226,7 @@ void MatrixPower<MatrixType>::computeIntPower(const PlainObject& b, ResultType&
     else if (p>0) {
       m_tmp1 = m_A;
     }
-    else if (b.cols() * (pp - applyings) <= m_A.cols() * squarings) {
+    else if (m_A.cols() > 2 && b.cols()*(pp-applyings) <= m_A.cols()*squarings) {
       PartialPivLU<MatrixType> A(m_A);
       res = A.solve(b);
       for (--pp; pp >= 1; --pp)
@@ -237,7 +237,7 @@ void MatrixPower<MatrixType>::computeIntPower(const PlainObject& b, ResultType&
       m_tmp1 = m_A.inverse();
     }
 
-    while (b.cols() * (pp - applyings) > m_A.cols() * squarings) {
+    while (b.cols()*(pp-applyings) > m_A.cols()*squarings) {
       if (std::fmod(pp, 2) >= 1) {
 	apply(b, res, init);
 	--applyings;