Using trapz doesn't work
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Hey Guys,
I already read some answers about 'errors using trapz' but i didn't get what's wrong because the lengths of my vektors are similiar. All vectors have the size 1x24000 double, thus dX_dTeta is also 1x24000 double. I need to integrate the function F. Are there any mistakes in it?
Thanks!!!
Here is my code:
%% sektion
for i = 1:(ceil((T_H2O_ein-T_H2O_aus)/h))
dX_dTeta(i) = cp_H2O * Massenstromverhaeltnis(i) * ((X_sat(i) - X_vektor(i))/(h_Luft_sat(i)...
- h_Luft_vektor(i) + ((0.865^(2/3)*(((0.622+X_sat(i))/(0.622+X_vektor(i))-1)/...
(log((0.622+X_sat(i))/(0.622+X_vektor(i))))))-1)*(h_Luft_sat(i) - h_Luft_vektor(i) -...
(X_sat(i) - X_vektor(i))*(h_verdampfung + cp_Dampf*T_H2O_vektor(i))) - ...
(X_sat(i) - X_vektor(i))*cp_H2O * T_H2O_vektor(i)));
end
temp = linspace(19,43,24000);
F = dX_dTeta(i)/(X_sat(i)-X_vektor(i));
for i = 1:integrationsende
NTU = trapz(temp,F,1);
end
1 comentario
Jakob B. Nielsen
el 31 de En. de 2020
First, what does your 2nd for loop do? You dont have i anywhere in the loop.
Second - without knowing your various variable values it is hard for us to run the code and see the error you get - so can you either post the error, or include your values in the code strip you posted?
Respuestas (1)
J. Alex Lee
el 31 de En. de 2020
F is of size 1x1, not 1x24000
10 comentarios
J. Alex Lee
el 1 de Feb. de 2020
Hmm, you might want to re-think your overall strategy. What do you mean you "solved" the upper equation? Eq. 20 and 21 look like coupled ODE...what do the double primes mean
and
? Second derivatives? What are your boundary conditions? Is it possible to combine Eqs. 20, 21, and 22 into a single ODE or integral, or express Eq. 22 differently based on Eqs. 20 and 21?
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/269430/image.png)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/269431/image.png)
But for the problem at hand of trapz not appearing to work when it seems like it should, can you provide the variables temp and F in a .mat file?
In general, trapz should be replaceable by manually doing a trapezoid rule, but your suggestion doesn't make a whole lot of sense to me, based on your original inputs being temp and FF...
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