diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 091edaef2..3455e99b7 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -13,9 +13,18 @@ build-and-test:
   stage: test
   image: ubuntu:24.04
   timeout: 4 hours
+  parallel:
+    matrix:
+      - UG_BUILD_ID: build-gcc-13
+        UG_C_COMPILER: "gcc"
+        UG_CXX_COMPILER: "g++"
+      - UG_BUILD_ID: build-clang-15
+        UG_C_COMPILER: "clang-15"
+        UG_CXX_COMPILER: "clang++-15"
+  #tags:
+  #  - ${PROVIDER}-${STACK}
+  #environment: $PROVIDER/$STACK
   variables:
-    CMAKE_C_COMPILER: "gcc"
-    CMAKE_CXX_COMPILER: "g++"
     UGHUB_DIR: "$CI_PROJECT_DIR/ughub"
     UG4_OLD_DIR: "$CI_PROJECT_DIR/ug4-old"
     UG4_NEW_DIR: "$CI_PROJECT_DIR/ug4-new"
@@ -23,7 +32,7 @@ build-and-test:
     - echo "Setting up base ug4 enviroment."
     - mkdir -p $UG4_NEW_DIR/ugcore
     - mv * $UG4_NEW_DIR/ugcore || true
-    - apt-get update >/dev/null && apt-get install -y python3 git cmake build-essential >/dev/null
+    - apt-get update >/dev/null && apt-get install -y python3 git cmake build-essential clang-15 >/dev/null
     - cd $CI_PROJECT_DIR && git clone https://gitlab.com/ug4-project/ughub.git
     - export PATH="$PATH:$UGHUB_DIR"
     - mkdir $UG4_OLD_DIR && cd $UG4_OLD_DIR
@@ -36,12 +45,12 @@ build-and-test:
     - cp --update=none -R $UG4_OLD_DIR/* $UG4_NEW_DIR
     # build ug4 in release
     - cd $UG4_NEW_DIR
-    - mkdir -p build && cd build
-    - cmake .. -DENABLE_ALL_PLUGINS=ON -DDEBUG=OFF -DCMAKE_BUILD_TYPE=Release
+    - mkdir -p $UG_BUILD_ID && cd $UG_BUILD_ID
+    - cmake .. -DENABLE_ALL_PLUGINS=ON -DDEBUG=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=$UG_CXX_COMPILER -DCMAKE_C_COMPILER=$UG_C_COMPILER
     - make -j 4
     # build testsuite
     - cd $UG4_NEW_DIR/apps/unit_tests
-    - mkdir -p build && cd build
+    - mkdir -p $UG_BUILD_ID && cd $UG_BUILD_ID
     - cmake .. -DUSE_JSON=OFF -DINTERNAL_BOOST=ON -DDEBUG=OFF -DCMAKE_BUILD_TYPE=Release
     - make -j 4
     - cd $UG4_NEW_DIR
@@ -54,10 +63,11 @@ build-and-test:
     paths:
       - $UG4_NEW_DIR/report.xml
       - $UG4_NEW_DIR/test.log
+      # - $UG4_NEW_DIR/lib/*
       - $UG4_NEW_DIR/bin/*
       - $UG4_NEW_DIR/bin/plugins/*
     reports:
-      junit: report.xml
+      junit: $UG4_NEW_DIR/report.xml
 
 # BUILD sources on various platforms and compilers
 deploy-docker:
diff --git a/ugbase/bridge/algebra_bridges/ordering_bridge.cpp b/ugbase/bridge/algebra_bridges/ordering_bridge.cpp
index de722c051..8804b086b 100644
--- a/ugbase/bridge/algebra_bridges/ordering_bridge.cpp
+++ b/ugbase/bridge/algebra_bridges/ordering_bridge.cpp
@@ -44,7 +44,7 @@
 #include "lib_algebra/lib_algebra.h"
 
 // ordering algorithms
-#include "lib_algebra/ordering_strategies/algorithms/ordering_algorithms.cpp"
+#include "lib_algebra/ordering_strategies/algorithms/ordering_algorithms.h"
 
 using namespace std;
 
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h b/ugbase/lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h
index 3602fbe87..631e71227 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h
@@ -30,8 +30,8 @@
  * GNU Lesser General Public License for more details.
  */
 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_IORDERING_ALGORITHM__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_IORDERING_ALGORITHM__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_IORDERINGALGORITHM_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_IORDERINGALGORITHM_H
 
 #include "common/util/smart_pointer.h"
 
@@ -76,6 +76,6 @@ class IOrderingAlgorithm{
 	virtual const char* name() const = 0;
 };
 
-} //namespace
+}
 
-#endif //guard
+#endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.h
similarity index 96%
rename from ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.cpp
rename to ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.h
index a60ff00c0..f714c02a6 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/SCC_ordering.h
@@ -30,8 +30,8 @@
  * GNU Lesser General Public License for more details.
  */
 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_SCC_ORDERING__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_SCC_ORDERING__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_SCC_ORDERING_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_SCC_ORDERING_H
 
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/graph_traits.hpp>
@@ -41,8 +41,8 @@
 #include <boost/graph/strong_components.hpp>
 
 #include "IOrderingAlgorithm.h"
-#include "topological_ordering.cpp"
-#include "util.cpp"
+#include "topological_ordering.h"
+#include "util.h"
 #include "lib_algebra/algebra_common/permutation_util.h"
 
 //debug
@@ -233,7 +233,7 @@ class SCCOrdering : public IOrderingAlgorithm<TAlgebra, O_t>
 };
 
 
-} //namespace
+}
 
 
-#endif //guard
+#endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.h
similarity index 96%
rename from ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.cpp
rename to ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.h
index 4f56ddea0..47122454a 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/boost_cuthill_mckee_ordering.h
@@ -30,8 +30,8 @@
  * GNU Lesser General Public License for more details.
  */
  
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_BOOST_CUTHILL_MCKEE_ORDERING__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_BOOST_CUTHILL_MCKEE_ORDERING__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_BOOST_CUTHILL_MCKEE_ORDERING_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_BOOST_CUTHILL_MCKEE_ORDERING_H
 
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/graph_traits.hpp>
@@ -40,7 +40,7 @@
 #include <boost/graph/cuthill_mckee_ordering.hpp>
 
 #include "IOrderingAlgorithm.h"
-#include "util.cpp"
+#include "util.h"
 
 //debug
 #include "common/error.h"
@@ -200,6 +200,6 @@ class BoostCuthillMcKeeOrdering : public IOrderingAlgorithm<TAlgebra, O_t>
 	bool m_bReverse;
 };
 
-} //namespace
+}
 
-#endif //guard
+#endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.h
similarity index 95%
rename from ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.cpp
rename to ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.h
index fb819ecda..95e2c795d 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/boost_minimum_degree_ordering.h
@@ -30,8 +30,8 @@
  * GNU Lesser General Public License for more details.
  */
  
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_BOOST_MINIMUM_DEGREE_ORDERING__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_BOOST_MINIMUM_DEGREE_ORDERING__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_BOOST_MINIMUM_DEGREE_ORDERING_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_BOOST_MINIMUM_DEGREE_ORDERING_H
 
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/graph_traits.hpp>
@@ -40,7 +40,7 @@
 #include <boost/graph/minimum_degree_ordering.hpp>
 
 #include "IOrderingAlgorithm.h"
-#include "util.cpp"
+#include "util.h"
 
 //debug
 #include "common/error.h"
@@ -170,6 +170,6 @@ class BoostMinimumDegreeOrdering final : public IOrderingAlgorithm<TAlgebra, O_t
 	O_t o;
 };
 
-} //namespace
+}
 
-#endif //guard
+#endif
\ No newline at end of file
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/iters.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/iters.cpp
index 626045571..78e3a5562 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/iters.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/iters.cpp
@@ -29,11 +29,9 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Lesser General Public License for more details.
  */
- 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_ITERS__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_ITERS__
 
 #include <tuple>
+#include <vector>
 
 namespace ug{
 
@@ -192,4 +190,3 @@ std::tuple<non_dirichlet_iterator<TAlgebra>, non_dirichlet_iterator<TAlgebra> >
 
 } //namespace
 
-#endif //guard
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.cpp
index 20ec2df21..afe2adc55 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.cpp
@@ -1,5 +1,3 @@
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_ORDERING_CPP__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_ORDERING_CPP__
 
 #include "common/common.h"
 #include "common/profiler/profiler.h"
@@ -294,5 +292,3 @@ void ComputeCuthillMcKeeOrder(std::vector<size_t>& vNewIndex,
 }
 
 }
-
-#endif //guard
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.h b/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.h
index e6f11f6d0..f0f31fdbc 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.h
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/native_cuthill_mckee.h
@@ -31,13 +31,13 @@
  */
 
 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_ORDERING__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_ORDERING__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_NATIVE_CUTHILL_MCKEE_H
 
 #include <vector>
 
 #include "IOrderingAlgorithm.h"
-#include "util.cpp"
+#include "util.h"
 
 //debug
 #include "common/error.h"
@@ -179,6 +179,6 @@ class NativeCuthillMcKeeOrdering : public IOrderingAlgorithm<TAlgebra, O_t>
 };
 
 
-} // end namespace ug
+}
 
 #endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.cpp
deleted file mode 100644
index b5ee041ab..000000000
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.cpp
+++ /dev/null
@@ -1,6 +0,0 @@
-#include "boost_cuthill_mckee_ordering.cpp"
-#include "boost_minimum_degree_ordering.cpp"
-#include "native_cuthill_mckee.h"
-#include "topological_ordering.cpp"
-
-#include "SCC_ordering.cpp"
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.h b/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.h
new file mode 100644
index 000000000..e0fa3e7d9
--- /dev/null
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/ordering_algorithms.h
@@ -0,0 +1,10 @@
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_ORDERING_ALGORITHMS_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_ORDERING_ALGORITHMS_H
+
+#include "boost_cuthill_mckee_ordering.h"
+#include "boost_minimum_degree_ordering.h"
+#include "native_cuthill_mckee.h"
+#include "topological_ordering.h"
+#include "SCC_ordering.h"
+
+#endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.h
similarity index 97%
rename from ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.cpp
rename to ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.h
index bb788b5a0..45f95ac29 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/topological_ordering.h
@@ -30,8 +30,8 @@
  * GNU Lesser General Public License for more details.
  */
 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_TOPOLOGICAL_ORDERING__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_TOPOLOGICAL_ORDERING__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_TOPOLOGICAL_ORDERING_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_TOPOLOGICAL_ORDERING_H
 
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/graph_traits.hpp>
@@ -47,7 +47,7 @@
 #include <deque>
 
 #include "IOrderingAlgorithm.h"
-#include "util.cpp"
+#include "util.h"
 
 //debug
 #include "common/error.h"
@@ -288,6 +288,6 @@ class TopologicalOrdering : public IOrderingAlgorithm<TAlgebra, O_t>
 	O_t o;
 };
 
-} //namespace
+}
 
-#endif //guard
+#endif
diff --git a/ugbase/lib_algebra/ordering_strategies/algorithms/util.cpp b/ugbase/lib_algebra/ordering_strategies/algorithms/util.h
similarity index 85%
rename from ugbase/lib_algebra/ordering_strategies/algorithms/util.cpp
rename to ugbase/lib_algebra/ordering_strategies/algorithms/util.h
index f99c1fd71..166b354d7 100644
--- a/ugbase/lib_algebra/ordering_strategies/algorithms/util.cpp
+++ b/ugbase/lib_algebra/ordering_strategies/algorithms/util.h
@@ -1,6 +1,6 @@
 
-#ifndef __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_UTIL__
-#define __UG__LIB_ALGEBRA__ORDERING_STRATEGIES_ALGORITHMS_UTIL__
+#ifndef UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_UTIL_H
+#define UG_BASE_LIB_ALGEBRA_ORDERING_STRATEGIES_ALGORITHMS_UTIL_H
 
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/graph_traits.hpp>
@@ -51,6 +51,6 @@ bool is_permutation(O_t &o){
 
 #endif
 
-} //namespace
+}
 
-#endif //guard
+#endif
diff --git a/ugbase/lib_disc/ordering_strategies/algorithms/directional_ordering.cpp b/ugbase/lib_disc/ordering_strategies/algorithms/directional_ordering.cpp
index ea748185d..f82d5ef79 100644
--- a/ugbase/lib_disc/ordering_strategies/algorithms/directional_ordering.cpp
+++ b/ugbase/lib_disc/ordering_strategies/algorithms/directional_ordering.cpp
@@ -48,7 +48,7 @@
 #include "lib_disc/spatial_disc/user_data/user_data.h"
 
 #include "lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h"
-#include "lib_algebra/ordering_strategies/algorithms/util.cpp"
+#include "lib_algebra/ordering_strategies/algorithms/util.h"
 
 #include <assert.h>
 #include "common/error.h"
diff --git a/ugbase/lib_disc/ordering_strategies/algorithms/lexorder.h b/ugbase/lib_disc/ordering_strategies/algorithms/lexorder.h
index 593a82d4f..c3e7ececa 100644
--- a/ugbase/lib_disc/ordering_strategies/algorithms/lexorder.h
+++ b/ugbase/lib_disc/ordering_strategies/algorithms/lexorder.h
@@ -41,7 +41,7 @@
 #include "lib_disc/function_spaces/grid_function.h"
 
 #include "lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h"
-#include "lib_algebra/ordering_strategies/algorithms/util.cpp"
+#include "lib_algebra/ordering_strategies/algorithms/util.h"
 #include "lib_disc/function_spaces/dof_position_util.h"
 
 #include "common/error.h"
diff --git a/ugbase/lib_disc/ordering_strategies/algorithms/riverorder.h b/ugbase/lib_disc/ordering_strategies/algorithms/riverorder.h
index cafbb9d4a..bec04e28e 100644
--- a/ugbase/lib_disc/ordering_strategies/algorithms/riverorder.h
+++ b/ugbase/lib_disc/ordering_strategies/algorithms/riverorder.h
@@ -45,7 +45,7 @@
 #include "lib_disc/function_spaces/grid_function.h"
 
 #include "lib_algebra/ordering_strategies/algorithms/IOrderingAlgorithm.h"
-#include "lib_algebra/ordering_strategies/algorithms/util.cpp"
+#include "lib_algebra/ordering_strategies/algorithms/util.h"
 
 #include "common/error.h"