Build instructions for ICON Model (release-2025.10-public)

apps/ICON-AES/ARCHER2_2025.10_gcc11.2.md

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+# ICON Model Build Instructions on ARCHER2
+
+These instructions describe how to build `libfyaml` and the `ICON model (release-2025.10-public)` on ARCHER2 using the GNU Programming Environment and
+GCC 11.2.0.
+
+---
+
+## 1. Environment
+
+These instructions assume a standard ARCHER2 environment.
+
+### 1.1 Modules
+
+```bash
+module load PrgEnv-gnu
+module load gcc/11.2.0
+module load cray-python
+module load cray-hdf5 cray-netcdf libxml2
+```
+
+### 1.2 Working directory
+
+```bash
+cd ${HOME/home/work}
+```
+
+All software will be built in this directory tree.
+
+### 1.3 Python environment
+
+Creating a python virtual environment for helpful packages.
+
+```bash
+python -m venv --system-site-packages venv
+source venv/bin/activate
+pip install cython==3.2.4 jinja2 netCDF4 wheel
+```
+
+---
+
+## 2. Build libfyaml (v0.9.3)
+
+ICON requires `libfyaml`, which is not provided as a system module on ARCHER2.
+
+### 2.1 Download and unpack
+
+```bash
+wget https://github.com/pantoniou/libfyaml/releases/download/v0.9.3/libfyaml-0.9.3.tar.gz
+tar xzvf libfyaml-0.9.3.tar.gz
+```
+
+### 2.2 Configure and build
+
+```bash
+cd ${HOME/home/work}/libfyaml-0.9.3
+
+export LIBFYAML_ROOT=${HOME/home/work}/libfyaml-0.9.3
+mkdir ${LIBFYAML_ROOT}/build
+
+autoreconf -f -i
+
+${LIBFYAML_ROOT}/configure \
+  CC=cc CXX=CC FC=ftn \
+  --prefix=${LIBFYAML_ROOT}/build
+
+make -j8
+make install
+```
+
+This installs libfyaml under:
+
+```
+${LIBFYAML_ROOT}/build
+```
+
+---
+
+## 3. Build ICON Model (release-2025.10-public)
+
+### 3.1 Obtain source code
+
+```bash
+cd ${HOME/home/work}
+
+git clone -b release-2025.10-public --recursive \
+  https://gitlab.dkrz.de/icon/icon-model.git
+```
+
+### 3.2 Configure and build
+
+```bash
+cd ${HOME/home/work}/icon-model
+
+export ICON_MODEL_ROOT=${HOME/home/work}/icon-model
+mkdir ${ICON_MODEL_ROOT}/build
+
+autoreconf -f -i
+```
+
+The following include paths are required for HDF5, NetCDF, MPI, libxml2, and libfyaml:
+
+```bash
+export ICON_INCLUDES="-I${HDF5_DIR}/include/ \
+  -I${NETCDF_DIR}/include/ \
+  -I${CRAY_MPICH_DIR}/include/ \
+  -I${LIBXML2_DIR}/include/ \
+  -I${LIBFYAML_ROOT}/build/include/"
+```
+
+Configure step
+
+```bash
+${ICON_MODEL_ROOT}/configure \
+  CC=cc CXX=CC FC=ftn F77=ftn \
+  LDFLAGS="-L${HDF5_DIR}/lib/ \
+    -L${NETCDF_DIR}/lib/ \
+    -L${CRAY_MPICH_DIR}/lib/ \
+    -L${LIBXML2_DIR}/lib/ \
+    -L${LIBFYAML_ROOT}/build/lib/ \
+    -Wl,-rpath,${LIBFYAML_ROOT}/build/lib" \
+  LIBS='-lnetcdff -lnetcdf -lhdf5 -lmpifort -lmpi -lxml2 -lfyaml' \
+  FCFLAGS="${ICON_INCLUDES} -cpp -std=gnu -fmodule-private -fimplicit-none -fmax-identifier-length=63 \
+    -ffree-line-length-132 -O3 -ffast-math -D__LOOP_EXCHANGE -fallow-argument-mismatch" \
+  CFLAGS="${ICON_INCLUDES} -std=gnu99 -O2 -DHAVE_LIBNETCDF -DHAVE_NETCDF4 -D__XE6__ -DgFortran" \
+  CPPFLAGS="${ICON_INCLUDES}" \
+  MPI_LAUNCH="srun" \
+  MPIROOT="${CRAY_MPICH_DIR}" \
+  --enable-bundled-python \
+  --enable-openmp \
+  --disable-mpi-checks \
+  --prefix="${ICON_MODEL_ROOT}/build"
+```
+
+Build and install ICON
+
+```bash
+make -j8
+make install
+```
+
+The ICON executables and supporting files will be installed under:
+
+```
+${ICON_MODEL_ROOT}/build
+```
+
+---
+
+## 4. Notes
+
+- These instructions assume the compiler wrappers (`cc`, `ftn` and `CC`) are
+  used throughout.
+- The build enables `OpenMP` support.