fix findEigen3 in CMakeLists

Remove manual way (old fashion) of finding Eigen3 with an own-defined FindEigen.cmake.

The recommended procedure is defined here: https://eigen.tuxfamily.org/dox/TopicCMakeGuide.html

by using FindEigen3 and EIGEN3_INCLUDE_DIR in CMakeLists.txt

cmake_modules/FindEigen.cmake

-# Ceres Solver - A fast non-linear least squares minimizer
-# Copyright 2015 Google Inc. All rights reserved.
-# http://ceres-solver.org/
-#
-# Redistribution and use in source and binary forms, with or without
-# modification, are permitted provided that the following conditions are met:
-#
-# * Redistributions of source code must retain the above copyright notice,
-#   this list of conditions and the following disclaimer.
-# * Redistributions in binary form must reproduce the above copyright notice,
-#   this list of conditions and the following disclaimer in the documentation
-#   and/or other materials provided with the distribution.
-# * Neither the name of Google Inc. nor the names of its contributors may be
-#   used to endorse or promote products derived from this software without
-#   specific prior written permission.
-#
-# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-# POSSIBILITY OF SUCH DAMAGE.
-#
-# Author: alexs.mac@gmail.com (Alex Stewart)
-#
-
-# FindEigen.cmake - Find Eigen library, version >= 3.
-#
-# This module defines the following variables:
-#
-# EIGEN_FOUND: TRUE iff Eigen is found.
-# EIGEN_INCLUDE_DIRS: Include directories for Eigen.
-#
-# EIGEN_VERSION: Extracted from Eigen/src/Core/util/Macros.h
-# EIGEN_WORLD_VERSION: Equal to 3 if EIGEN_VERSION = 3.2.0
-# EIGEN_MAJOR_VERSION: Equal to 2 if EIGEN_VERSION = 3.2.0
-# EIGEN_MINOR_VERSION: Equal to 0 if EIGEN_VERSION = 3.2.0
-#
-# The following variables control the behaviour of this module:
-#
-# EIGEN_INCLUDE_DIR_HINTS: List of additional directories in which to
-#                          search for eigen includes, e.g: /timbuktu/eigen3.
-#
-# The following variables are also defined by this module, but in line with
-# CMake recommended FindPackage() module style should NOT be referenced directly
-# by callers (use the plural variables detailed above instead).  These variables
-# do however affect the behaviour of the module via FIND_[PATH/LIBRARY]() which
-# are NOT re-called (i.e. search for library is not repeated) if these variables
-# are set with valid values _in the CMake cache_. This means that if these
-# variables are set directly in the cache, either by the user in the CMake GUI,
-# or by the user passing -DVAR=VALUE directives to CMake when called (which
-# explicitly defines a cache variable), then they will be used verbatim,
-# bypassing the HINTS variables and other hard-coded search locations.
-#
-# EIGEN_INCLUDE_DIR: Include directory for CXSparse, not including the
-#                    include directory of any dependencies.
-
-# Called if we failed to find Eigen or any of it's required dependencies,
-# unsets all public (designed to be used externally) variables and reports
-# error message at priority depending upon [REQUIRED/QUIET/<NONE>] argument.
-macro(EIGEN_REPORT_NOT_FOUND REASON_MSG)
-  unset(EIGEN_FOUND)
-  unset(EIGEN_INCLUDE_DIRS)
-  # Make results of search visible in the CMake GUI if Eigen has not
-  # been found so that user does not have to toggle to advanced view.
-  mark_as_advanced(CLEAR EIGEN_INCLUDE_DIR)
-  # Note <package>_FIND_[REQUIRED/QUIETLY] variables defined by FindPackage()
-  # use the camelcase library name, not uppercase.
-  if (Eigen_FIND_QUIETLY)
-    message(STATUS "Failed to find Eigen - " ${REASON_MSG} ${ARGN})
-  elseif (Eigen_FIND_REQUIRED)
-    message(FATAL_ERROR "Failed to find Eigen - " ${REASON_MSG} ${ARGN})
-  else()
-    # Neither QUIETLY nor REQUIRED, use no priority which emits a message
-    # but continues configuration and allows generation.
-    message("-- Failed to find Eigen - " ${REASON_MSG} ${ARGN})
-  endif ()
-  return()
-endmacro(EIGEN_REPORT_NOT_FOUND)
-
-# Search user-installed locations first, so that we prefer user installs
-# to system installs where both exist.
-#
-# TODO: Add standard Windows search locations for Eigen.
-list(APPEND EIGEN_CHECK_INCLUDE_DIRS
-  /usr/local/include
-  /usr/local/homebrew/include # Mac OS X
-  /opt/local/var/macports/software # Mac OS X.
-  /opt/local/include
-  /usr/include)
-# Additional suffixes to try appending to each search path.
-list(APPEND EIGEN_CHECK_PATH_SUFFIXES
-  eigen3 # Default root directory for Eigen.
-  Eigen/include/eigen3 ) # Windows (for C:/Program Files prefix).
-
-# Search supplied hint directories first if supplied.
-find_path(EIGEN_INCLUDE_DIR
-  NAMES Eigen/Core
-  PATHS ${EIGEN_INCLUDE_DIR_HINTS}
-  ${EIGEN_CHECK_INCLUDE_DIRS}
-  PATH_SUFFIXES ${EIGEN_CHECK_PATH_SUFFIXES})
-
-if (NOT EIGEN_INCLUDE_DIR OR
-    NOT EXISTS ${EIGEN_INCLUDE_DIR})
-  eigen_report_not_found(
-    "Could not find eigen3 include directory, set EIGEN_INCLUDE_DIR to "
-    "path to eigen3 include directory, e.g. /usr/local/include/eigen3.")
-endif (NOT EIGEN_INCLUDE_DIR OR
-       NOT EXISTS ${EIGEN_INCLUDE_DIR})
-
-# Mark internally as found, then verify. EIGEN_REPORT_NOT_FOUND() unsets
-# if called.
-set(EIGEN_FOUND TRUE)
-
-# Extract Eigen version from Eigen/src/Core/util/Macros.h
-if (EIGEN_INCLUDE_DIR)
-  set(EIGEN_VERSION_FILE ${EIGEN_INCLUDE_DIR}/Eigen/src/Core/util/Macros.h)
-  if (NOT EXISTS ${EIGEN_VERSION_FILE})
-    eigen_report_not_found(
-      "Could not find file: ${EIGEN_VERSION_FILE} "
-      "containing version information in Eigen install located at: "
-      "${EIGEN_INCLUDE_DIR}.")
-  else (NOT EXISTS ${EIGEN_VERSION_FILE})
-    file(READ ${EIGEN_VERSION_FILE} EIGEN_VERSION_FILE_CONTENTS)
-
-    string(REGEX MATCH "#define EIGEN_WORLD_VERSION [0-9]+"
-      EIGEN_WORLD_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
-    string(REGEX REPLACE "#define EIGEN_WORLD_VERSION ([0-9]+)" "\\1"
-      EIGEN_WORLD_VERSION "${EIGEN_WORLD_VERSION}")
-
-    string(REGEX MATCH "#define EIGEN_MAJOR_VERSION [0-9]+"
-      EIGEN_MAJOR_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
-    string(REGEX REPLACE "#define EIGEN_MAJOR_VERSION ([0-9]+)" "\\1"
-      EIGEN_MAJOR_VERSION "${EIGEN_MAJOR_VERSION}")
-
-    string(REGEX MATCH "#define EIGEN_MINOR_VERSION [0-9]+"
-      EIGEN_MINOR_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
-    string(REGEX REPLACE "#define EIGEN_MINOR_VERSION ([0-9]+)" "\\1"
-      EIGEN_MINOR_VERSION "${EIGEN_MINOR_VERSION}")
-
-    # This is on a single line s/t CMake does not interpret it as a list of
-    # elements and insert ';' separators which would result in 3.;2.;0 nonsense.
-    set(EIGEN_VERSION "${EIGEN_WORLD_VERSION}.${EIGEN_MAJOR_VERSION}.${EIGEN_MINOR_VERSION}")
-  endif (NOT EXISTS ${EIGEN_VERSION_FILE})
-endif (EIGEN_INCLUDE_DIR)
-
-# Set standard CMake FindPackage variables if found.
-if (EIGEN_FOUND)
-  set(EIGEN_INCLUDE_DIRS ${EIGEN_INCLUDE_DIR})
-endif (EIGEN_FOUND)
-
-# Handle REQUIRED / QUIET optional arguments and version.
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(Eigen
-  REQUIRED_VARS EIGEN_INCLUDE_DIRS
-  VERSION_VAR EIGEN_VERSION)
-
-# Only mark internal variables as advanced if we found Eigen, otherwise
-# leave it visible in the standard GUI for the user to set manually.
-if (EIGEN_FOUND)
-  mark_as_advanced(FORCE EIGEN_INCLUDE_DIR)
-endif (EIGEN_FOUND)