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diff --git a/third_party/eigen3/Eigen/src/Householder/BlockHouseholder.h b/third_party/eigen3/Eigen/src/Householder/BlockHouseholder.h
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+++ b/third_party/eigen3/Eigen/src/Householder/BlockHouseholder.h
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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2010 Vincent Lejeune
+// Copyright (C) 2010 Gael Guennebaud <gael.guennebaud@inria.fr>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef EIGEN_BLOCK_HOUSEHOLDER_H
+#define EIGEN_BLOCK_HOUSEHOLDER_H
+
+// This file contains some helper function to deal with block householder reflectors
+
+namespace Eigen { 
+
+namespace internal {
+
+/** \internal */
+template<typename TriangularFactorType,typename VectorsType,typename CoeffsType>
+void make_block_householder_triangular_factor(TriangularFactorType& triFactor, const VectorsType& vectors, const CoeffsType& hCoeffs)
+{
+  typedef typename TriangularFactorType::Index Index;
+  typedef typename VectorsType::Scalar Scalar;
+  const Index nbVecs = vectors.cols();
+  eigen_assert(triFactor.rows() == nbVecs && triFactor.cols() == nbVecs && vectors.rows()>=nbVecs);
+
+  for(Index i = 0; i < nbVecs; i++)
+  {
+    Index rs = vectors.rows() - i;
+    Scalar Vii = vectors(i,i);
+    vectors.const_cast_derived().coeffRef(i,i) = Scalar(1);
+    triFactor.col(i).head(i).noalias() = -hCoeffs(i) * vectors.block(i, 0, rs, i).adjoint()
+                                       * vectors.col(i).tail(rs);
+    vectors.const_cast_derived().coeffRef(i, i) = Vii;
+    // FIXME add .noalias() once the triangular product can work inplace
+    triFactor.col(i).head(i) = triFactor.block(0,0,i,i).template triangularView<Upper>()
+                             * triFactor.col(i).head(i);
+    triFactor(i,i) = hCoeffs(i);
+  }
+}
+
+/** \internal */
+template<typename MatrixType,typename VectorsType,typename CoeffsType>
+void apply_block_householder_on_the_left(MatrixType& mat, const VectorsType& vectors, const CoeffsType& hCoeffs)
+{
+  typedef typename MatrixType::Index Index;
+  enum { TFactorSize = MatrixType::ColsAtCompileTime };
+  Index nbVecs = vectors.cols();
+  Matrix<typename MatrixType::Scalar, TFactorSize, TFactorSize, ColMajor> T(nbVecs,nbVecs);
+  make_block_householder_triangular_factor(T, vectors, hCoeffs);
+
+  const TriangularView<const VectorsType, UnitLower>& V(vectors);
+
+  // A -= V T V^* A
+  Matrix<typename MatrixType::Scalar,VectorsType::ColsAtCompileTime,MatrixType::ColsAtCompileTime,0,
+         VectorsType::MaxColsAtCompileTime,MatrixType::MaxColsAtCompileTime> tmp = V.adjoint() * mat;
+  // FIXME add .noalias() once the triangular product can work inplace
+  tmp = T.template triangularView<Upper>().adjoint() * tmp;
+  mat.noalias() -= V * tmp;
+}
+
+} // end namespace internal
+
+} // end namespace Eigen
+
+#endif // EIGEN_BLOCK_HOUSEHOLDER_H