[mesa-users] Undocumented control in &controls: eos_partials_consistency_level

[Warrick Ball]

Hi everyone,

I'm still tinkering with solar models and noticed that I get quite a big 
difference if I switch the opacity interpolation between linear and cubic 
in X and Z.  Motivated by the recent thread on the interpolation of the 
EoS [1] I tried digging around inside the EoS module to see what options 
were available for deciding which interpolation to use in the EoS.

Along the way, I came across the control eos_partials_consistency_level in 
&controls.  The documentation is empty [2] and the only test cases that 
change its value from the default -1 are ccsn_IIp and envelope_inflation 
(both of which set it to 1).  I assume consistency refers to thermodynamic 
consistency.  My question to the forum is: what does this control do?

In principle, if I work through the code for long enough I should be 
able to figure out what's going on.  But it'll be much faster if someone 
else could explain it...  Just searching for consistency_level in 
$MESA_DIR/eos/private/eosdt_eval.f90, it looks to me that as 
consistency_level increases, so the order of derivatives that are 
thermodynamically consistent increases too.  At consistency_level = 1 or 
2, the first derivatives are made consistent, and for consistency_level = 
3, the second derivatives are made consistent too.  I don't understand 
what happens above level 4, though.  My suspicion is that a different kind 
of interpolation is implemented for levels 4, 5 and 6 but I'm hoping 
someone can correct me.

Cheers,
Warrick

[1] https://sourceforge.net/p/mesa/mailman/message/35754574/
[2] http://mesa.sourceforge.net/controls_defaults.html#eos_partials_consistency_level


------------
Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
wball at bison.ph.bham.ac.uk
+44 (0)121 414 4552