  This document is one of the deliverable reports created for the ESCAPE
project. ESCAPE stands for Energy-efficient Scalable Algorithms for Weather
Prediction at Exascale. The project develops world-class, extreme-scale
computing capabilities for European operational numerical weather prediction
and future climate models. This is done by identifying Weather & Climate dwarfs
which are key patterns in terms of computation and communication (in the spirit
of the Berkeley dwarfs). These dwarfs are then optimised for different hardware
architectures (single and multi-node) and alternative algorithms are explored.
Performance portability is addressed through the use of domain specific
languages.
  Atlas has been presented in deliverable D1.3. With this deliverable D2.3, a
first version of the Atlas software libraries is publicly released with a
permissive open-source license. The software is freely available for download,
and contains a user guide and installation instructions.
  The Atlas libraries have been carefully designed with the user's perspective
in mind. Even though Atlas is mainly coded in C++, an equivalent Fortran
interface is presented without additional runtime overhead. The Fortran
interfaces are provided to accommodate existing NWP and climate models that
typically consist of Fortran subroutines. The mixed Fortran/C++ design enhances
interoperability between NWP and climate models and novel data management
techniques. Atlas provides interoperability with accelerator hardware, and can
serve as foundation to support higher level abstractions as used in domain
specific languages.
