simplify low mass convective star

[zingale]

No description provided.

[zingale]

for some reason, this gives rather large diffs compared to the original version, even though they should be the same to tolerances.

[zingale]

I think that the reason this fails is that doing eos_input_ps is only doing the root finding on the thermodynamics / EOS part. It does not account for the fact that changing rho also changes HSE. For this setup, we seem to be very sensitive to that, and if we just use the EOS to zero things, then we get convergence on the thermodynamics without then having to adjust the dynamics, it seems.

So I think that the correct way to do this is as implemented.

It also suggests that for the other problems, we should be doing the same thing and not relying on eos_input_ps