A copy-paste of the Executive Summary: This document examines risks associated with relying on Fortran for codes critical to nuclear security into the late 203

A copy-paste of the Executive Summary: This document examines risks associated with relying on Fortran for codes critical to nuclear security into the late 2030s. The study was requested by the LANL ASC program office to support its decisions. To date, much of the discussion about the prospects for Fortran has tended to be informal and centered on questions (such as, “will the language be around in 20 years”) that are impossible to answer with any certainty. By focusing on estimates of the likelihood associated with different outcomes, rather than on specific predictions, we hope to clarify points of disagreement within the community and strengthen the analytic basis for reasoning about the future. Our assessment for seven distinct risks associated with continued use of Fortran are that in the next fifteen years: 1. It is very likely that we will be unable to staff Fortran projects with top-rate computer scientists and computer engineers. 2. There is an even chance that we will be unable to staff Fortran projects with top-rate computational scientists and physicists. 3. There is an even chance continued maintenance of Fortran codes will lead to expensive human or financial maintenance costs. 4. It is very unlikely that codes that rely on Fortran will have poor performance on future CPU technologies. 5. It is likely that codes that rely on Fortran will have poor performance for GPU technologies. 6. It is very likely that Fortran will preclude effective use of important advances in computing technology. 7. There is an even chance that Fortran will inhibit introduction of new features or physics that can be introduced with other languages.