  As the Science Mission Directorate contemplates establishing an open code
policy, we consider it timely to share our experiences as the developers of the
open-source partial differential equation solver Dedalus. Dedalus is a flexible
framework for solving partial differential equations. Its development team
primarily uses it for studying stellar and planetary astrophysics. Dedalus was
developed originally for astrophysical fluid dynamics (AFD), though it has
found a much broader user base, including applied mathematicians, plasma
physicists, and oceanographers. Here, we will focus on issues related to
open-source software from the perspective of AFD. We use the term AFD with the
understanding that astrophysics simulations are inherently multi-physics: fluid
dynamics coupled with some combination of gravitational dynamics, radiation
transfer, relativity, and magnetic fields. In practice, a few well-known
open-source simulation packages represent a large fraction of published work in
the field. However, we will argue that an open-code policy should encompass not
just these large simulation codes, but also the input files and analysis
scripts. It is our interest that NASA adopt an open-code policy because without
it, reproducibility in computational science is needlessly hampered.
