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This repository contains a stand-alone kernel for the c_sw subroutine, extracted from the FV3 model. The goal of this repository is to facilitate direct comparisons of different implementations of c_sw. Alternative implementations may use different programming languages, parallel programming models, or numerical modeling libraries. They may also target different hardware such as GPUs or ARM processors. In numerical modeling, metrics for comparison traditionally include performance and portability. However, this work encourages comparison of developer productivity and design metrics such as ease of use, extensibility, and maintainability.

A Fortran 90 implementation of c_sw is provided as a baseline reference to which other implementations should be compared. Additional implementations will be added as they are developed.

This repository is organized as follows.

Contains the reference input and output data all implementations must use for testing and validation.

Contains the source tree for the reference implementation. See the README in that directory for details about how to run and test it.

Alternative implementations will be stored in a new top-level subdirectory along side the reference implementation. In this documentation, foo/ is simply a place holder for names given to future implementations.

Contributors who wish to provide an alternative implementation of c_sw must do so by issuing a Pull Request to the develop branch from their own forks of this repository. Write access to this repository can not be granted.

All pull requests to this repository must include:

• A build system that functions across platforms and (if applicable) across multiple compilers.
• Source code that is well written, properly formatted, and documented.
• A test suite that passes and duplicates the tests that are run in the reference implementation. At present, 11 digits of accuracy are expected.
• A GitHub Actions configuration to automate the new implementation's test suite.
• A documentation README.md describing the new implementation, including how to run and test it.