Using the values of du in the rhs! function

I recently came across the necessity of needing the values of the parameter du (rate of change of some variables) for calculating the numerical fluxes and/or the source terms. As far as I checked, this could be possible by changing the input parameters for many inner functions and also their order (particularly for the reset_du!). However, I am not sure about the cost penalties in terms of performance in doing so and, it also could not be a practical solution. I would like to know what you thought about this issue and if there is another easier solution that did not occur to me. Thank you in advance for the help.

Cheers

Start by tracing rhs! and reset_du!, the inner functions named in the issue, and review the existing comment discussion. Determine how du is currently propagated and whether numerical fluxes or source terms need it. Done would require an agreed design, an implementation that exposes du where needed, and evidence that performance remains acceptable.

Written by the indexing model from the issue text.