Using temperature and pressure data to estimate antoine coefficients for glycerol
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I am trying to estimate the antoine coefficients using the nlinfit function form the statistics toolbox, I am getting some errors when trying to run this code, could somebody please help me get this to work and estimate the antoine coefficients i would really appreciate it.
antoine = @(T,p) (log10(p) - A + B/(T+C));
beta0 = [3.93737,1411.531,-200.566];
beta = [A,B,C];
beta = nlinfit(T,p,antoine,beta0);
Error using nlinfit (line 213)
Error evaluating model function '@(T,p)(log10(p)-A+B/(T+C))'.
Error in Temperatureconversion (line 55)
beta = nlinfit(T,p,antoine,beta0);
Caused by:
Error using /
Matrix dimensions must agree.
0 Comments
Answers (2)
Star Strider
on 10 Jan 2022
Since both variable are present in the objective function equation, nlinfit (or lsqcurvefit) are not really good choices for this.
A regular optimization function (such as fminsearch) would work best. (There are other optionis, however everyone has fminsearch.)
% % % DATA MATRIX MAPPING — T = Tp(:,1), p = Tp(:,2)
Tp = [270:10:320; rand(1,6)].'; % Data Matrix
% % % ANTOINE FUNCTION MAPPING — b(1) = A, b(2) = B, b(3) = C
antoine = @(b,Tp) (log10(Tp(:,2)) - b(1) + b(2)/(Tp(:,1)+b(3)));
beta0 = [3.93737,1411.531,-200.566];
[beta,fv] = fminsearch(@(b)norm(antoine(b,Tp)), beta0);
fprintf('A =\t%10.4f\nB =\t%10.4f\nC =\t%10.4f\nfv =\t%10.4f',[beta,fv])
Having the actual data would produce the best results, however the created data demonstrate that the approach works.
.
11 Comments
Torsten
on 10 Jan 2022
in my physical chemistry labs as an undergraduate our values were often quite good and gave a good fit to the functions with little error
Lucky you !
Star Strider
on 10 Jan 2022
We were just compulsive! All of us were doing out best to get into med school, so every little bit helped.
Torsten
on 10 Jan 2022
antoine = @(b,T) 10.^( b(1) + b(2)./(T+b(3)));
beta0 = [3.93737,1411.531,-200.566];
beta = nlinfit(T,p,antoine,beta0)
5 Comments
Torsten
on 10 Jan 2022
nlinfit starts to evaluate antoine with beta0.
To see what happens, try
vec = antoine(beta0,T)
before you call nlinfit.
Take care that all elements in "vec" are real numbers (no infinity or NaN) by varying beta0.
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