Example Playground

Table of Contents

• Building Examples
  • Via CMake (recommended)
  • Adding a New Example
  • Equivalent g++ Commands
• Available Examples
  • ex_array_basic
  • ex_geom_mesh
  • ex_cfv_solver

The examples/ directory contains compilable C++ programs that exercise the code patterns described in the documentation guides. Drop a new .cpp file into examples/ and it is automatically picked up by CMake – no manual registration needed.

Building Examples

Via CMake (recommended)

# Build all examples at once:
cmake --build build -t examples -j32
 
# Build a single example:
cmake --build build -t ex_array_basic -j32
 
# Run (most examples need MPI):
mpirun -np 2 build/examples/ex_array_basic
mpirun -np 1 build/examples/ex_geom_mesh
mpirun -np 1 build/examples/ex_cfv_solver

Examples are EXCLUDE_FROM_ALL, so they are not built by a plain cmake --build build. You must name them explicitly or use the examples aggregate target.

Adding a New Example

Create a file in examples/ matching one of these naming patterns:

Filename prefix	Linked libraries	Use when
ex_array_*	dnds	Array, ParArray, ArrayTransformer
ex_geom_*	geom + dnds	Mesh, elements, quadrature
ex_cfv_*	cfv + geom + dnds	FiniteVolume, VR, ModelEvaluator
ex_euler_*	euler_library_NS + cfv + geom + dnds	Euler evaluator, gas dynamics

The examples/CMakeLists.txt glob discovers ex_*.cpp files automatically via CONFIGURE_DEPENDS.

Equivalent g++ Commands

If you want to compile an example outside of CMake (e.g. for a quick test on a cluster), here are the equivalent commands. Adjust paths to match your installation.

Paths (set these for your environment):

DNDSR_SRC=/path/to/DNDSR/src
DNDSR_BUILD=/path/to/DNDSR/build
DNDSR_EXT=/path/to/DNDSR/external
CFD_EXT=$DNDSR_EXT/cfd_externals/install
MPI_DIR=$(dirname $(dirname $(which mpicxx)))

ex_array_basic (links only dnds):

mpicxx -std=c++17 -O2 \
    -I$DNDSR_SRC \
    -I$DNDSR_EXT/eigen \
    -I$DNDSR_EXT/nlohmann \
    -I$DNDSR_EXT/boost \
    -I$DNDSR_EXT/fmt/include \
    -I$DNDSR_EXT/nanoflann \
    -I$DNDSR_EXT/cppcodec \
    -I$DNDSR_EXT/argparse/include/argparse \
    -I$DNDSR_EXT/CGAL/include \
    -I$CFD_EXT/include \
    -DNINSERT -D__DNDS_REALLY_COMPILING__ \
    -fopenmp \
    examples/ex_array_basic.cpp \
    -L$DNDSR_BUILD/src/DNDS -ldnds \
    -L$DNDSR_BUILD/fmt -lfmt \
    -L$CFD_EXT/lib -lcgns -lhdf5 -lparmetis -lmetis -lz \
    -lstdc++fs -ldl \
    -o ex_array_basic

ex_geom_mesh (links geom + dnds):

mpicxx -std=c++17 -O2 \
    -I$DNDSR_SRC \
    -I$DNDSR_EXT/eigen -I$DNDSR_EXT/nlohmann -I$DNDSR_EXT/boost \
    -I$DNDSR_EXT/fmt/include -I$DNDSR_EXT/nanoflann \
    -I$DNDSR_EXT/cppcodec -I$DNDSR_EXT/argparse/include/argparse \
    -I$DNDSR_EXT/CGAL/include -I$CFD_EXT/include \
    -DNINSERT -D__DNDS_REALLY_COMPILING__ -fopenmp \
    examples/ex_geom_mesh.cpp \
    -L$DNDSR_BUILD/src/Geom -lgeom \
    -L$DNDSR_BUILD/src/DNDS -ldnds \
    -L$DNDSR_BUILD/fmt -lfmt \
    -L$CFD_EXT/lib -lcgns -lhdf5 -lparmetis -lmetis -lz \
    -lstdc++fs -ldl \
    -o ex_geom_mesh

ex_cfv_solver (links cfv + geom + dnds):

mpicxx -std=c++17 -O2 \
    -I$DNDSR_SRC \
    -I$DNDSR_EXT/eigen -I$DNDSR_EXT/nlohmann -I$DNDSR_EXT/boost \
    -I$DNDSR_EXT/fmt/include -I$DNDSR_EXT/nanoflann \
    -I$DNDSR_EXT/cppcodec -I$DNDSR_EXT/argparse/include/argparse \
    -I$DNDSR_EXT/CGAL/include -I$CFD_EXT/include \
    -DNINSERT -D__DNDS_REALLY_COMPILING__ -fopenmp \
    examples/ex_cfv_solver.cpp \
    -L$DNDSR_BUILD/src/CFV -lcfv \
    -L$DNDSR_BUILD/src/Geom -lgeom \
    -L$DNDSR_BUILD/src/DNDS -ldnds \
    -L$DNDSR_BUILD/fmt -lfmt \
    -L$CFD_EXT/lib -lcgns -lhdf5 -lparmetis -lmetis -lz \
    -lstdc++fs -ldl \
    -o ex_cfv_solver

Notes:

• Replace mpicxx with your MPI C++ wrapper (e.g. mpicxx, mpiCC).
• Add -I/usr/local/cuda-XX/include and -lcudart if your build has CUDA enabled.
• The static libraries (libdnds.a, libgeom.a, libcfv.a) must be built first with CMake. The g++ commands link against the already built libraries in the build tree.

Available Examples

ex_array_basic

Guide: Array Usage Guide

Demonstrates the core array infrastructure:

• Fixed-row Array (compile-time width)
• Dynamic-row Array (runtime width)
• CSR Array with compress/decompress
• ParArray ghost communication with ArrayTransformer
• ArrayPair with BorrowAndPull

mpirun -np 2 build/examples/ex_array_basic

ex_geom_mesh

Guide: Geometry + CFV Usage Guide

Demonstrates mesh building and geometric queries:

• CGNS file reading and mesh construction pipeline
• Element type queries (GetCellElement)
• Node coordinate access
• Face traversal and boundary detection
• Quadrature integration to compute cell volumes

mpirun -np 1 build/examples/ex_geom_mesh

ex_cfv_solver

Guides: Geometry + CFV Usage Guide (Parts 5–9)

Demonstrates the full CFV solver pipeline:

• Mesh building from a periodic CGNS file
• VariationalReconstruction settings and construction
• ConstructMetrics, ConstructBaseAndWeight, ConstructRecCoeff
• DOF array allocation (BuildUDof, BuildURec)
• Initial condition from cell barycenters
• Iterative VR reconstruction (5 sweeps)
• RHS evaluation via ModelEvaluator

mpirun -np 1 build/examples/ex_cfv_solver