Sensitivities of PoKiTT expressions & testing
- Constant-pressure simulations (e.g. flamelets) using PoKiTT expressions and implicit time integration will require sensitivities in the heat capacity, density, species enthalpy, and mixture molecular weight expressions. We need support for these sensitivities, and they should be tested. Simple expressions like density, pressure, temperature, and mixture molecular weight can easily be compared to computed values. At the very least, we should have an executable that triggers sensitivities of all expressions with a sensitivity method.
The analytical Jacobian does not need to be included on new sensitivity tests as it is tested against gold standards already.
- The analytical Jacobian for production rates sensitivities requires that density, temperature, and mass fractions are included in the sensitivity variables. If they are not, but mass fraction sensitivities are triggered, then an exception for an unregistered field will be thrown. I'm not sure of any way to catch this. We should at least have a test that exposes this behavior, and that ensures proper behavior in the case that density, temperature, and mass fractions are not the ONLY sensitivity variables. That has never been attempted in an application...
To summarize: add support for sensitivities of more PoKiTT expressions, add a test for those that can be easily tested, and add testing to ensure proper behavior of sensitivities and the analytical Jacobian.