[PATCH 3/2] gas model: add polynomials for Z factors of oxygen/nitrogen/helium

[Linus Torvalds]

On Mar 2, 2016 7:34 PM, "Steve" <kg7je at comcast.net> wrote:
>
> SMB:  Would be interesting to see if a polynomial of 21% of the oxygen
> factors and 79% of nitrogen factors comes close (enough) to the air
> specific one.

See some of my "Google is great at graphing" emails.

Short version: yes, the linear mixing seems to give extremely good
results at least for air (which is the only one we have independent
tables for). There are bigger differences just between the air tables
on Wikipedia and baue.

In fact, if you plot the baue air polynomial and the "air mix"
polynomial at the same time, you get an almost *perfect* match to 300
bar.

After that it diverges a bit, but that seems to be because the oxygen
polynomial really ends up being bad at 300+ bar.

You can trivially test yourself: just paste this into google:

 y = 0.9994355774568318-0.00035668306234655186*x+0.00000218474273138185*x^2+5.8403793405e-9*x^3-2.780101081e-11*x^4+3.144563e-14*x^5,
 y = 0.21*(1.0002231211532653-0.0007471497056767194*x+0.00000200444854807816*x^2+2.91501995188e-9*x^3-4.48294663e-12*x^4-6.11529e-15*x^5)+
     0.79*(1.0001898816185364-0.00030793319362077315*x+0.00000327557417347714*x^2-1.93872574476e-9*x^3-2.7732353e-12*x^4-2.8921e-16*x^5)
    from 0 to 500

where that first "y=" is the polynomial from the "air" table at baue,
the second "y=" is the "air mix" from the polynomials for oxygen and
nitrogen.

They are literally on top of each other.

In fact, it's *such* a perfect match up to 275 bar that I wonder if
the baue numbers aren't based on a linear mix.

In other words, it's possible that one or more of the the baue tables
aren't entirely experimental. Mayeb the baue pure gas tables are
experimental, and the air table is from a linear mix of those?

Regardless, the linear mix looks really good. When you compare it to
the Wikipedia numbers, it's still pretty close. So everything lines up
pretty well.

                   Linus