Getting started » Downloading and building

Operating sytem

Atlas requires a POSIX compliant operating system. This includes:

• Linux
• MacOSX (Darwin)

Compilers

Atlas requires a C++ compiler that supports the C++11 standard. The optional Atlas Fortran API requires a Fortran compiler that supports the Fortran 2008 standard.

Tested compilers include:

• GNU 6.3, 7.3, 8.3
• Intel 18, 19
• PGI 17.7, 19.10
• Cray 8.7
• Clang C++ 7, 9 + GNU Fortran

CMake

• Minimum required version: 3.6 or greater
• Recommended version: 3.14 or greater

CMake is often already available on your system. If version requirements are incompatible, prebuilt CMake binary distribution may be downloaded here

Required dependencies

For C++ API of Atlas:

• C++ compiler: C++11 standard support required
• CMake: Build system (meta-build system) used to compile Atlas
• ecbuild: It implements some CMake macros that are used within the Atlas build system. For more brief information and to install, check the ecbuild installation instructions
• eckit: It implements some useful C++ functionalities useful for Atlas. For more brief information and to install, check the eckit installation instructions

For Fortran API of Atlas, additional required dependencies:

• Fortran compiler: Fortran 2008 standard support required.
• fckit : It implements some useful Fortran functionalities. This is only needed when Fortran bindings are required. For more brief information and to install, check the fckit installation instructions
• Python : Required to generate Fortran interfaces

Optional dependencies

• MPI: Required for distributed memory parallelisation.
• OpenMP: Required for shared memory parallelisation. For use see. As OpenMP is implemented within compilers, it is not possible to install it yourself.
• CGAL: Required for enabling tesselation using Delaunay triangulation of unstructured grids.
• Eigen3 : Linear algebra library that should not impact any Atlas internal performance.
• FFTW – FFT library that improves efficiency of inverse spherical harmonics transforms (TransLocal). (Version 3.3.4 minimum required)
• BLAS / LAPACK – Linear Algebra libraries that improve efficiency of inverse spherical harmonics transforms (TransLocal). This library is typically available on the system, and preferred implementation is available within Intels MKL library.
• transi – For enabling IFS spherical harmonics transforms (TransIFS). This exposes an MPI parallel implementation for both direct and inverse spherical harmonics transforms. Note that transi is currently not open-source and requires a license agreement with ECMWF! For more brief information and to install, check the transi installation instructions
• GridTools – For enabling GPU capability using CUDA in C++ or OpenACC in Fortran (compiler permitting).
• Proj – For enabling Proj4 projections for grids. This is allows for projections that are not natively supported in Atlas.

Downloading Atlas

atlas is officially maintained and available from its ECMWF github page.

The master branch tracks the latest stable release, whereas the develop branch tracks the latest developments.

To download the project at the latest release we can type on the terminal the commands reported below:

git clone -b master https://github.com/ecmwf/atlas.git

Building Atlas

The atlas build system is based on CMake which tries to automatically detect compilers and project dependencies. To avoid suprises make sure that the following environment variables are pointing to the correct compiler.

• CC – Path to C compiler
• CXX – Path to C++ compiler
• Fortran – Path to Fortran compiler

Other environment variables which may help CMake (version greater than 3.12) in finding required and optional dependencies for Atlas:

• ecbuild_ROOT – Path to ecbuild install prefix
• eckit_ROOT – Path to eckit install prefix
• fckit_ROOT – Path to fckit install prefix
• transi_ROOT – Path to transi install prefix
• GridTools_ROOT – Path to GridTools install prefix
• CGAL_ROOT – Path to CGAL install prefix
• FFTW_ROOT – Path to FFTW install prefix
• PROJ4_ROOT – Path to Proj install prefix
• Eigen3_ROOT – Path to Eigen install prefix

atlas can be configured and installed as follows, to a given path-to-install as shown below:

cd atlas
mkdir build && cd build
cmake ../ -DCMAKE_INSTALL_PREFIX=<path-to-install>
make -j8

The number 8 in the argument -j8 to make speeds up compilation by using 8 threads. This number can be tuned to maximise compilation speed.

Testing Atlas

The Atlas tests are managed by ctest which is bundled with the CMake software. To launch the tests, navigate to the build directory and execute

ctest --output-on-failure

To run only tests matching a certain regular expression, execute

ctest --output-on-failure -R <regex>

To get output from tests that pass, execute

Installing Atlas

To install atlas, navigate to the build directory, and simply execute

make install