Merge branch 'update_build' into 'master'

Update build system, externals

See merge request !5

.clang-format

 ---
 Language:        Cpp
+
+ColumnLimit:     90                   # line width, 0: respect programmer's choice
+TabWidth:        8
+UseTab:          Never
+
 AccessModifierOffset: -2
 AlignAfterOpenBracket: Align
 AlignConsecutiveAssignments: false
@@ -16,7 +21,6 @@ AllowShortLoopsOnASingleLine: true
 AlwaysBreakAfterDefinitionReturnType: None
 AlwaysBreakAfterReturnType: None
 AlwaysBreakBeforeMultilineStrings: true
-AlwaysBreakTemplateDeclarations: true
 BinPackArguments: true
 BinPackParameters: true
 BraceWrapping:
@@ -36,7 +40,7 @@ BreakBeforeBraces: Attach
 BreakBeforeTernaryOperators: true
 BreakConstructorInitializersBeforeComma: true
 # BreakInheritanceListBeforeComma: true
-ColumnLimit:     90
+
 CommentPragmas:  '^ IWYU pragma:'
 ConstructorInitializerAllOnOneLineOrOnePerLine: false
 ConstructorInitializerIndentWidth: 4
@@ -53,6 +57,7 @@ IncludeCategories:
     Priority:        2
   - Regex:           '.*'
     Priority:        3
+SortIncludes:    false
 IndentCaseLabels: true
 IndentWidth:     2
 IndentWrappedFunctionNames: false
@@ -72,7 +77,6 @@ PenaltyExcessCharacter: 1000000
 PenaltyReturnTypeOnItsOwnLine: 200
 PointerAlignment: Left
 ReflowComments:  true
-SortIncludes:    true
 SpaceAfterCStyleCast: false
 SpaceBeforeAssignmentOperators: true
 SpaceBeforeParens: ControlStatements
@@ -84,6 +88,8 @@ SpacesInCStyleCastParentheses: false
 SpacesInParentheses: false
 SpacesInSquareBrackets: false
 Standard:        Auto
-TabWidth:        8
-UseTab:          Never
+
+# If true, always break after the template<...> of a template declaration.
+AlwaysBreakTemplateDeclarations: true
+
 ...

.gitmodules

+[submodule "modules/data"]
+	path = modules/data
+	url = ../../AirShowerPhysics/corsika-data
+	branch = master
+        shallow = true
+[submodule "externals/spdlog"]
+	path = externals/spdlog
+	url = https://github.com/gabime/spdlog.git
+        shallow = true
+[submodule "modules/proposal"]
+	path = modules/proposal
+	url = https://github.com/tudo-astroparticlephysics/PROPOSAL.git
+	branch = restructure_parametrization
+        shallow = true
+[submodule "modules/conex"]
+	path = modules/conex
+	url = ../../AirShowerPhysics/cxroot
+	branch = master
+        shallow = true

AUTHORS

-Maximilian Reininghaus, maximilian.reininghaus@kit.edu
-Ralf Ulrich, ralf.ulrich@kit.edu
-Felix Riehn, friehn@lip.pt

COLLABORATION_AGREEMENT.md

@@ -13,7 +13,7 @@ examples of other big scientific software projects.
 
 The CORSIKA project consists of the contributions from the scientific
 community and individuals in a best effort to deliver the best
-possible computing performance and physics output. 
+possible performance and physics output. 
 The MCnet guidelines developed by [www.montecarlonet.org](www.montecarlonet.org) 
 are copied in [MCNET_GUIDELINES](MCNET_GUIDELINES) -- they provide a very good 
 additional scope that contributors should read and consider. 
@@ -23,82 +23,41 @@ liability and licensing question are only handled by the adopted
 software license.
 
 ## The software license of the CORSIKA project
+
 The license adopted for the CORSIKA project is the explicit copyleft
 license GPLv3, as copied in full in the file
 [LICENSE](LICENSE). Each source file of the CORSIKA project contains a
 short statement of the copyright and this license. Each binary or
-source code release of CORSIKA must contain the file LICENSE. The
-code, documentation and content in the folder [ThirdParty](ThirdParty)
+source code release of CORSIKA contains the file LICENSE. The
+code, documentation and content in the folder [externals](externals)
 is not integral part of the CORSIKA project and can be based on, or
 include, other licenses, which must be compatible with GPLv3. Check the
 content of this folder for details and additional license information. It depends on the configuration of
 the build system to what extend this code is used to build CORSIKA.
 
-## Who is the "copyright holder"
-For legal reasons and the ability to maintain the CORSIKA project
-effectively over a very long lifespan of several decades, all
-contributors are required to transfer their copyright to the CORSIKA
-Project. Of course you will be duly credited and your name will appear
-on the contributors page and in the [AUTHORS](AUTHORS) file shipped
-with every binary and source distribution. The copyright transfer is
-necessary to be able to effectively defend the project in case of
-litigation. The copyright holder may change, if decided by the CORSIKA
-Project. The current copyright holder is the CORSIKA Project
-corsika-project@lists.kit.edu, with the current chair person 
-Ralf Ulrich (KIT) ralf.ulrich@kit.edu.
-
-## Definition of a "contributor"
-Contributor is a person of whom at least one merge request was
-accepted for the master branch of the CORSIKA project at
-[https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika](https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika).
-All contributors will be co-listed and credited as (software) authors
-of the CORSIKA project, as well as listed indefinitely in the
-[AUTHORS](AUTHORS) file. Contributors should add their name and
-contact data to the [AUTHORS](AUTHORS) file, as part of one of their
-merge requests. This file is always distributed together with all
-source and binary releases.  If you contribute to any non-master
-branch, you can add your name to the [AUTHORS](AUTHORS) file of this
-particular branch, but all official releases are normally performed
-via the master branch.
+
+## Contributing
 
 If you want to contribute, you need to read
 [the GUIDELINES](CONTRIBUTING.md) and comply with these rules, or help to
-improve them.
+improve them. 
 
 
-## The CORSIKA Project panel
-The CORSIKA Project panel makes all decisions for the CORSIKA
-Project. It can also change the
+## The CORSIKA Projects Maintainers
+The CORSIKA Project mainters make all decisions for the CORSIKA
+Project. They can also change the
 [COLLABORATION\_AGREEMENT](COLLABORATION\_AGREEMENT.md), the
 [GUIDELINES](CONTRIBUTING.md) or any other structure or document relevant for the CORSIKA Project.
 
-The CORSIKA Project *panel* consists (October 2018) of
-   
-  * Hans Dembinski (MPG)
-  * Ralph Engel (KIT)
-  * Dieter Heck (KIT)
-  * Tanguy Pierog (KIT)
-  * Maximilian Reininghaus (KIT)
-  * Felix Riehn (LIP)
-  * Ralf Ulrich (KIT)
-  * Darko Veberic (KIT)
-  
-and can be contacted via corsika-project@lists.kit.edu.  The chair
-person of the CORSIKA Project is Ralf Ulrich (KIT). Members of the
-CORSIKA Project *panel* can be *Maintainer* of the CORSIKA Project in
-gitlab at
-[https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika](https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika),
-and have special responsibilities also for this reason. 
+The current CORSIKA Project maintainers are listed in the file [MAINTAINERS](MAINTAINERS.md). 
 
-### Changing to a different license, for parts, or the complete project
+and can be contacted via corsika-project@lists.kit.edu.  The chair
+person of the CORSIKA Project is Ralf Ulrich (KIT). Maintainers have special 
+responsibilities for specific parts of the project. 
 
-The CORSIKA Project panel can change the license for parts or the entire project in general or for individual releases.
 
 ### Planning and performing releases
 
-The CORSIKA Project panel decides on releases of the software, and about the content of it. 
+The CORSIKA maintainers decide on releases of the software, and about the content of it. 
 
-### Changes to the Collaboration Agreement
 
-The CORSIKA Project panel decides on changes to the Collaboration
-agreement.

CONTRIBUTING.md

@@ -8,7 +8,7 @@ change/improve them.
 
 # How to contribute
 
-  - We organize all development via `Issues` that may be feature requests,
+  - We organize all development via gitlab `Issues` that may be feature requests,
     ideas, discussions, or bugs fix requests. 
   - New issues can be created, or existing issues
     picked up or contributed to. 
@@ -19,7 +19,8 @@ change/improve them.
     created directly via the gitlab web interface. 
   - Proposed code to close one issue (located in a specific git
     branch) is reviewed, discussed, and eventually merged
-    into the master branch to close the issue.
+    into the master branch via a merge-request (MR) to close the issue.
+  - all merge request will undergo a code review, and must be approved before merge, in order to ensure high code qualtiy: [Code Approval Procedure](https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika/-/wikis/Code-Approval-Procedure)
 
 
 ## Code formatting
@@ -31,9 +32,9 @@ formatting. We provide a script `do-clang-format.sh`, which can be
 very useful. But we urge everybody to integrate `clang-format` already
 on the level of your source code editor. See [the official
 page](https://clang.llvm.org/docs/ClangFormat.html) for information
-about `clang-format` and its editor integration. At least: run
-`do-clang-format.sh` prior to any `git add` command. Code with
-improper formatting will not be accepted for merging. 
+about `clang-format` and its editor integrations. At least: run
+`do-clang-format.sh` prior to any `git add/commit` command. Code with
+improper formatting will not be accepted for merging. It will trigger automatic warnings by the continuous integration (CI) system.
 
 The definition of source code format is written down in the file
 [.clang-format](.clang-format) and can be changed, if the CORSIKA
@@ -42,109 +43,34 @@ e.g. [link1](https://clangformat.com/) or
 [link2](https://zed0.co.uk/clang-format-configurator/).
 
 
-## Naming conventions
-
-While `clang-format` does the structural formatting, we still need to agree on naming conventions:
-
-  - Classes and structs start with capital letters
-  - Class member variables start with "f"
-  - Any static variable has a "g" prefix. A static member variable starts with "fg"
-  - Class member functions start with capital letters
-  - Any class getter begins with "Get", and setter with "Set". Logical getters start with "Is" or "Has".
-  - enums should be "enum class" and start with a capital "E"
-  - Function parameter names start with "v"
-
-  - We use namespaces to avoid clashes and to structure code
-    - *Everything* is part of the corsika namespace
-    - All classes and objects are encapsulated into suited sub-namespaces,
-      thus corsika, corsikaes, corsika::units, etc.
-    - Namespace names do not use capital letters.  
-    - Every header file is copied during build and install into
-      "include/corsika/[namespace]" which also means, each header file
-      can only provide definitions for a _single_ namespace. It is one
-      main purpose of namespaces to structure the location of header
-      files.
-    - Each header file uses an include protection that includes at
-      least the namespace name, and header file name, thus, `#ifndef
-      __include_geometry_Point_h__` or `#ifndef __geometry_Point_h__`,
-      or similar are acceptable.
-    - Header files should always be included with `<..>`, thus,
-      `#include <corsika/framework/geometry/Point.hpp>` since the build system
-      will always provide the correct include directives (and files
-      anyway cannot be found in file-system paths, which generally do
-      not follow the namespace naming conventions outlined
-      here).
-
-  - Header files are named after the main class (or object) they
-    define. This also means each header file name starts with a
-    capital letter.
-  
-
-## Coding rules
-
-  - Code may not introduce any compiler errors, or warnings (latter: on current CI runners)
-  - All unit tests must succeed at all times. If tests fail, code is not merged.
-  - We use C++17 concepts wherever useful and helpful
-  - On any major error or malfunction we throw an exception. This is needed and required for complex physics and shower debugging.
-  - We never catch exceptions for error handling, there might be very few special exceptions from this. We need to discuss such cases.
-  - Everything that should not change should be `const`
-  - Everything that does not need to be visible to the outside of a class/struct should be `private` or `protected`
-  - We prefer the use of references, wherever useful
-  - There cannot be any pointer in the interface of any class or object
-    exposed to outside users, there might be pointers for very special cases
-    inside of classes.
-  - When you contribute new code, or extend existing code, at the same time provide unit-tests for all functionality.
-  - When you contribute new physics algorithms, in addition you also need to provide a validation module
-  - Code must be documented with `doxygen` commands
-  
-## CMAKE formatting
-
-  - command are lower cases, e.g. ```set (...)```
-  - variables upper case, e.g. ```set (VAR1 Text)```
-
-Since cmake itself lacks structure almost entirely:
-  - put a space between command and start of parenthesis, e.g. ```command (...)``` 
-  - add two spaces for logical indent 
-    ```
-    if (condition)
-      do something
-    endif (condition)
-    ```
-  - break long lines to start with new keyword in new line (indented)
-    ```
-    install (
-      FILES ${CORSIKAstackinterface_HEADERS}
-      DESTINATION include/${CORSIKAstackinterface_NAMESPACE}
-      )  
-    ```
-  - add plenty of comments to all cmake code
-  - use expressive variables and functions
+## Coding rules, conventions and guidelines
+
+Please read the [Coding wiki page](https://gitlab.ikp.kit.edu/AirShowerPhysics/corsika/-/wikis/Coding-Conventions-and-Guidelines).
+
 
 ## Release versioning scheme
 
-Releases of CORSIKA are thought to be the baseline for larger scale
-testing, and full production.  The releases are numbered as x.y.z,
-starting with x=8 form the gitlab c++ version. X will only be
-incremented for major design or physics changes. The y index is
-updated for new official releases that normally contain improved or
-enhanced physics performance, and may also contain normal interface
+Releases of CORSIKA 8 are thought to be the baseline for larger scale
+validation, and full production.  The releases are numbered as x.y.z,
+starting with x=8, which will not be changed for CORSIKA 8. The y index is
+updated for new releases that normally contain improved or
+enhanced physics performance, and also interface
 changes to accomodate improvements. The z index can be updated more
 frequently for bug fixes or new features. Changes in z will not
-contain (major) interface changes, thus, production code will remain
-fully compatible within changes of z.  Special releases of CORSIKA can
-also have a tag name from git, e.g. as in the "milestone1" release.
+contain interface changes, thus, production code will remain
+fully compatible within changes of z.  Special releases of CORSIKA will
+also have a release names.
 
 
 # How to become scientific author of the CORSIKA Project
 
 The CORSIKA Project decides on who becomes scientific author. The
-following conditions are clearly sufficient, but not all of them are
+following conditions are sufficient, but not all of them are
 required all the time:
   - responsibility for a particular functionality or software/management part 
   - have read and follow these [GUIDELINES](CONTRIBUTING.md)
   - active in the CORSIKA Project, that means responsive to
     discussions and problems in corsika-devel@list.kit.edu or on https//gitlab.ikp.kit.edu, 
-    of relevant *Issues*,
-    or in (phone) meetings
-  - agreement to the [COLLABORATION_AGREEMENT](COLLABORATION_AGREEMENT.md) is strictly required
-  - the members of the CORSIKA Project panel agree
+    of relevant *Issues*, or in (phone) meetings
+  - agreement to the [COLLABORATION_AGREEMENT](COLLABORATION_AGREEMENT.md) 
+  - the members of the CORSIKA Project must agree

MAINTAINERS.md

+
+Maintainers of the CORSIKA8 project are collaborators actively taking
+care of code contributions, quality control, development, and related
+discussions. 
+
+General and infrastructure:
+- Ralf Ulrich <ralf.ulrich@kit.edu>, KIT
+- Maximilian Reininghaus <maximilian.reininghaus@kit.edu>, KIT
+- Hans Dembinski <hdembins@mpi-hd.mpg.de>, Dortmund
+- Antonio Augusto Alves Junior <antonio.junior@kit.edu>, KIT
+
+High performance, GPU: 
+- Dominik Baack <dominik.baack@tu-dortmund.de>, Dortmund
+- Antonio Augusto Alves Junior <antonio.junior@kit.edu>, KIT
+- Luisa Arrabito <arrabito@in2p3.fr>, Montpellier
+
+Electromagnetic models: 
+- Jean-Marco Alameddine <jean-marco.alameddine@udo.edu>, Dortmund
+- Jan Soedingrekso <jan.soedingrekso@tu-dortmund.de>, Dortmund
+- Maximilian Sackel <maximilian.sackel@udo.edu>, Dortmund
+
+Hadron models:
+- Felix Riehn <friehn@lip.pt>, Santiago/Lisbon
+- Anatoli Fedynitch <anatoli.fedynitch@icecube.wisc.edu> ICRR Tokyo
+
+Radio:
+- Remy Prechelt <prechelt@hawaii.edu> 
+- Tim Huege <tim.huege@kit.edu>, KIT
+
+Testing, containers:
+- Lukas Nellen <lukas@nucleares.unam.mx>
+

cmake/CorsikaUtilities.cmake

@@ -8,91 +8,6 @@
 # the license.
 #
 
-#################################################
-#
-# takes a list of input files and prepends a path
-#
-
-function (CORSIKA_PREPEND_PATH return prefix)
-  set (listVar "")
-  foreach (f ${ARGN})
-    list (APPEND listVar "${prefix}/${f}")
-  endforeach (f)
-  set (${return} "${listVar}" PARENT_SCOPE)
-endfunction (CORSIKA_PREPEND_PATH)
-
-
-#################################################
-#
-# use: CORSIKA_COPY_HEADERS_TO_NAMESPACE theLib theNamesapce header1.h header2.h ...
-#
-# creates a dependence of theLib on the presence of all listed header files in the
-# build-directory include/theNamespace directory
-#
-# if needed, create symbolic links from the source files to this build-directory location
-#
-# any path information from input filenames is stripped, IF path was specified it is used for the link destination, if NOT the link is relative to the CMAKE_CURRENT_SOURCE_DIR
-# 
-function (CORSIKA_COPY_HEADERS_TO_NAMESPACE for_library in_namespace)
-  set (HEADERS_BUILD "")
-  foreach (HEADER ${ARGN})
-    # find eventual path, and handle it specificly
-    get_filename_component (barename ${HEADER} NAME)
-    get_filename_component (baredir ${HEADER} DIRECTORY)
-    # remove path, prepend build-directory destination
-    list (APPEND HEADERS_BUILD "${PROJECT_BINARY_DIR}/include/${in_namespace}/${barename}")
-    # define source location, use path if specified, otherwise CMAKE_CURRENT_SOURCE_DIR
-    set (FROM_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-    if (NOT "${baredir}" STREQUAL "")
-      set (FROM_DIR ${baredir})
-    endif ()
-    # define command to perform the symbolic linking
-    add_custom_command (
-      OUTPUT ${PROJECT_BINARY_DIR}/include/${in_namespace}/${barename}
-      COMMAND ${CMAKE_COMMAND} -E make_directory ${PROJECT_BINARY_DIR}/include/${in_namespace}
-      COMMAND ${CMAKE_COMMAND} -E create_symlink ${FROM_DIR}/${barename} ${PROJECT_BINARY_DIR}/include/${in_namespace}/${barename}
-      COMMENT "Generate link: ${PROJECT_BINARY_DIR}/include/${in_namespace}/${barename}"
-      )
-  endforeach (HEADER)
-  
-  # main target for this build step, depends on header files in build area
-  add_custom_target (
-    ${for_library}_BUILD
-    DEPENDS ${HEADERS_BUILD}
-    )
-  
-  # connect the _BUILD target to the main (external) target
-  add_dependencies (${for_library} ${for_library}_BUILD)
-
-endfunction (CORSIKA_COPY_HEADERS_TO_NAMESPACE)
-
-
-
-
-#################################################
-#
-# use: CORSIKA_ADD_FILES_ABSOLUTE varname
-#
-# add list of filenames with absolute paths (pointing to CMAKE_SOURCE_DIR) to ${varname} in PARAENT_SCOPE
-# 
-
-macro (CORSIKA_ADD_FILES_ABSOLUTE varname)
-  file (RELATIVE_PATH _relPath "${PROJECT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
-  foreach (_src ${ARGN})
-    if (_relPath)
-      list (APPEND "${varname}" "${CMAKE_SOURCE_DIR}/${_relPath}/${_src}")
-    else()
-      list (APPEND "${varname}" "${CMAKE_SOURCE_DIR}/${_src}")
-    endif()
-  endforeach()
-  if (_relPath)
-    # propagate SRCS to parent directory
-    set ("${varname}" "${${varname}}" PARENT_SCOPE)
-  endif()
-endmacro(CORSIKA_ADD_FILES_ABSOLUTE)
-
-
-
 #################################################
 #
 # central macro to register unit tests in cmake
@@ -126,23 +41,23 @@ endmacro(CORSIKA_ADD_FILES_ABSOLUTE)
 # TEMPORARY: All sanitizers are currently globally disabled by default, to enable them,
 # set CORSIKA_SANITIZERS_ENABLED to TRUE.
 function (CORSIKA_ADD_TEST)
-  cmake_parse_arguments (PARSE_ARGV 1 _ "" "SANITIZE" "SOURCES")
-
+  cmake_parse_arguments (PARSE_ARGV 1 C8_ADD_TEST "" "SANITIZE" "SOURCES")
   set (name ${ARGV0})
 
-  if (NOT __SOURCES)
+  if (NOT C8_ADD_TEST_SOURCES)
     set (sources ${name}.cc)
   else ()
-    set (sources ${__SOURCES})
+    set (sources ${C8_ADD_TEST_SOURCES})
   endif ()
 
-  if (NOT __SANITIZE)
+  if (NOT C8_ADD_TEST_SANITIZE)
     set(sanitize "address,undefined")
   else ()
-    set(sanitize ${__SANITIZE})
+    set(sanitize ${C8_ADD_TEST_SANITIZE})
   endif ()
 
   add_executable (${name} ${sources})
+  target_link_libraries (${name} CORSIKA8 Catch2)
   target_compile_options (${name} PRIVATE -g) # do not skip asserts
   target_include_directories (${name} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
   file (MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/test_outputs/)
@@ -153,3 +68,55 @@ function (CORSIKA_ADD_TEST)
   endif ()
   add_test (NAME ${name} COMMAND ${name} -o ${PROJECT_BINARY_DIR}/test_outputs/junit-${name}.xml -s -r junit)
 endfunction (CORSIKA_ADD_TEST)
+
+
+#################################################
+#
+# central macro to register an examples in cmake
+#
+# Examples can be globally executed by 'make run_examples'
+#
+# 1) Simple use:
+# Pass the name of the test.cc file as the first
+# argument, without the ".cc" extention.
+#
+# Example: CORSIKA_REGISTER_EXAMPLE (doSomething)
+#
+# The TARGET doSomething must already exists,
+#    i.e. typically via add_executable (doSomething src.cc).
+#
+# Example: CORSIKA_ADD_EXAMPLE (testSomething
+#              RUN_OPTION "extra command line options"
+#              )
+#
+# In all cases, you can further customize the target with
+# target_link_libraries(testSomething ...) and so on.
+#
+function (CORSIKA_REGISTER_EXAMPLE)
+  cmake_parse_arguments (PARSE_ARGV 1 C8_EXAMPLE "" "" "RUN_OPTIONS")
+  set (name ${ARGV0})
+
+  if (NOT C8_EXAMPLE_RUN_OPTIONS)
+    set (run_options "")
+  else ()
+    set (run_options ${C8_EXAMPLE_RUN_OPTIONS})
+  endif ()
+
+  target_compile_options (${name} PRIVATE -g) # do not skip asserts
+  file (MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/example_outputs/)
+  if (TARGET run_examples)
+  else ()
+    add_custom_target (run_examples)
+  endif ()
+  add_dependencies (run_examples ${name})
+  # just run the command as-is
+  set (CMD ${CMAKE_CURRENT_BINARY_DIR}/${name} ${run_options})
+  add_custom_command (TARGET run_examples
+    POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E echo ""
+    COMMAND ${CMAKE_COMMAND} -E echo "**************************************"
+    COMMAND ${CMAKE_COMMAND} -E echo "*****   running example: ${name} " ${run_options} VERBATIM
+    COMMAND ${CMD} VERBATIM
+    WORKING_DIRECTORY ${PROJECT_BINARY_DIR}/example_outputs)
+  install (TARGETS ${name} DESTINATION share/examples)
+endfunction (CORSIKA_REGISTER_EXAMPLE)

cmake/FindEigen3.cmake

-# - Try to find Eigen3 lib
-#
-# This module supports requiring a minimum version, e.g. you can do
-#   find_package(Eigen3 3.1.2)
-# to require version 3.1.2 or newer of Eigen3.
-#
-# Once done this will define
-#
-#  EIGEN3_FOUND - system has eigen lib with correct version
-#  EIGEN3_INCLUDE_DIR - the eigen include directory
-#  EIGEN3_VERSION - eigen version