Merge branch 'upstream-Eigen3' into worktree-eigen5-update

* upstream-Eigen3:
  Eigen3 2026-04-30 (5a7cc61d)

# Conflicts:
#	Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h

Author: hjmjohnson

Modules/ThirdParty/Eigen3/src/itkeigen/.gitattributes

@@ -1,3 +1,9 @@
+*.sh                         eol=lf
+debug/msvc/*.dat             eol=crlf
+debug/msvc/*.natvis          eol=crlf
+
+# ITK fork: relax content-checks for the largest Eigen header so
+# UpdateFromUpstream.sh / KWStyle hooks do not reject the import.
 * -whitespace
 Eigen/src/misc/lapacke.h hooks-max-size=1500000
 Eigen/src/misc/lapacke.h hooks.MaxObjectKiB=2048

Modules/ThirdParty/Eigen3/src/itkeigen/CMakeLists.txt

@@ -35,7 +35,7 @@ Mozilla Public License Version 2.0
     means any form of the work other than Source Code Form.
 
 1.7. "Larger Work"
-    means a work that combines Covered Software with other material, in 
+    means a work that combines Covered Software with other material, in
     a separate file or files, that is not Covered Software.
 
 1.8. "License"

Modules/ThirdParty/Eigen3/src/itkeigen/COPYING.MPL2

@@ -1,6 +1,14 @@
-Eigen is primarily MPL2 licensed. See COPYING.MPL2 and these links:
-  http://www.mozilla.org/MPL/2.0/
-  http://www.mozilla.org/MPL/2.0/FAQ.html
+Eigen is primarily licensed under the Mozilla Public License 2.0.
+See LICENSE, COPYING.MPL2, and these links:
+  https://www.mozilla.org/MPL/2.0/
+  https://www.mozilla.org/MPL/2.0/FAQ.html
 
-Some files contain third-party code under BSD or other MPL2-compatible licenses,
-whence the other COPYING.* files here.
+Some files contain third-party code under permissive or otherwise
+MPL2-compatible licenses, hence the other COPYING.* files here. These
+include Apache-2.0, BSD-style notices, the MINPACK license, and the MORSE
+CMake module BSD-style notice in cmake/MORSE-Copyright.txt.
+
+Note that some optional external dependencies (e.g. FFTW, MPFR C++)
+are distributed under different licenses, including the GPL. Refer to
+the individual source files and their respective COPYING files for
+details.

Modules/ThirdParty/Eigen3/src/itkeigen/COPYING.README

@@ -0,0 +1,52 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// 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_ACCELERATESUPPORT_MODULE_H
+#define EIGEN_ACCELERATESUPPORT_MODULE_H
+
+#include "SparseCore"
+
+#include "src/Core/util/DisableStupidWarnings.h"
+
+/** \ingroup Support_modules
+ * \defgroup AccelerateSupport_Module AccelerateSupport module
+ *
+ * This module provides an interface to the Apple Accelerate library.
+ * It provides the seven following main factorization classes:
+ * - class AccelerateLLT: a Cholesky (LL^T) factorization.
+ * - class AccelerateLDLT: the default LDL^T factorization.
+ * - class AccelerateLDLTUnpivoted: a Cholesky-like LDL^T factorization with only 1x1 pivots and no pivoting
+ * - class AccelerateLDLTSBK: an LDL^T factorization with Supernode Bunch-Kaufman and static pivoting
+ * - class AccelerateLDLTTPP: an LDL^T factorization with full threshold partial pivoting
+ * - class AccelerateQR: a QR factorization
+ * - class AccelerateCholeskyAtA: a QR factorization without storing Q (equivalent to A^TA = R^T R)
+ *
+ * \code
+ * #include <Eigen/AccelerateSupport>
+ * \endcode
+ *
+ * In order to use this module, the Accelerate headers must be accessible from
+ * the include paths, and your binary must be linked to the Accelerate framework.
+ * The Accelerate library is only available on Apple hardware.
+ *
+ * Note that many of the algorithms can be influenced by the UpLo template
+ * argument. All matrices are assumed to be symmetric. For example, the following
+ * creates an LDLT factorization where your matrix is symmetric (implicit) and
+ * uses the lower triangle:
+ *
+ * \code
+ * AccelerateLDLT<SparseMatrix<float>, Lower> ldlt;
+ * \endcode
+ */
+
+// IWYU pragma: begin_exports
+#include "src/AccelerateSupport/AccelerateSupport.h"
+// IWYU pragma: end_exports
+
+#include "src/Core/util/ReenableStupidWarnings.h"
+
+#endif  // EIGEN_ACCELERATESUPPORT_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/AccelerateSupport

@@ -14,8 +14,6 @@
 #include "src/Core/util/DisableStupidWarnings.h"
 
 /** \defgroup Cholesky_Module Cholesky module
- *
- *
  *
  * This module provides two variants of the Cholesky decomposition for selfadjoint (hermitian) matrices.
  * Those decompositions are also accessible via the following methods:

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Cholesky

@@ -26,7 +26,7 @@
  * For the sake of completeness, this module also propose the two following classes:
  * - class CholmodSimplicialLLT
  * - class CholmodSimplicialLDLT
- * Note that these classes does not bring any particular advantage compared to the built-in
+ * Note that these classes do not bring any particular advantage compared to the built-in
  * SimplicialLLT and SimplicialLDLT factorization classes.
  *
  * \code