Complex results when using my annonymous function

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Michael Käufl
Michael Käufl 2020-1-27
评论： Star Strider 2020-1-27
Hey Guys,
I am using runge-kutta-method to integrate function 1, after that i integrate function 2. But I always get complex results for function 2 (except the first iteration). Can anybody tell my why it is how it is? All other variables make sense, so the error should be anywhere else.
Thank you!!
while betrag > tol
for i=1:integrationsende
T_H2O_vektor(i+1) = T_H2O_vektor(i)+h;
X_sat(i) = 0.622 * p_sat_Antoine(T_H2O_vektor(i))/(p - p_sat_Antoine(T_H2O_vektor(i)));
h_Luft_sat(i) = (cp_Luft + cp_Dampf * X_sat(i)) * (T_H2O_vektor(i))+X_sat(i)*h_verdampfung;
Massenstromverhaeltnis = M_H2O_ein/M_Luft*(1 - M_Luft/M_H2O_ein*(X_2 - X_vektor(i)));
%Funktion 1
f1 = @(T_H2O,h_Luft) cp_H2O * Massenstromverhaeltnis *(1+(X_sat(i)-X_vektor(i))*cp_H2O...
*T_H2O/(h_Luft_sat(i)- h_Luft +((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-(X_sat(i)-...
X_vektor(i))*(h_verdampfung +cp_Dampf*T_H2O)) - (X_sat(i) ...
- X_vektor(i))*cp_H2O*T_H2O));
l1 = f1((T_H2O_vektor(i) ),(h_Luft_vektor(i) ));
l2 = f1((T_H2O_vektor(i) + 0.5*h),(h_Luft_vektor(i) + 0.5*h*l1));
l3 = f1((T_H2O_vektor(i) + 0.5*h),(h_Luft_vektor(i) + 0.5*h*l2));
l4 = f1((T_H2O_vektor(i) + h),(h_Luft_vektor(i) + h*l3));
h_Luft_vektor(i+1) = h_Luft_vektor(i) + h/6*(l1+2*l2+2*l3+l4);
%Funktion 2
f2 = @(T_H2O,X) cp_H2O * Massenstromverhaeltnis * ((X_sat(i) - X)/(h_Luft_sat(i)...
- h_Luft_vektor(i) + ((0.865^(2/3)*(((0.622+X_sat(i))/(0.622+X)-1)/...
(log((0.622+X_sat(i))/(0.622+X)))))-1)*(h_Luft_sat(i) - ...
h_Luft_vektor(i) -(X_sat(i) - X)*(h_verdampfung + cp_Dampf*T_H2O))) ...
- (X_sat(i) - X)*cp_H2O * T_H2O);
k1 = f2((T_H2O_vektor(i) ),(X_vektor(i) ));
k2 = f2((T_H2O_vektor(i) + 0.5*h),(X_vektor(i) + 0.5*h*k1));
k3 = f2((T_H2O_vektor(i) + 0.5*h),(X_vektor(i) + 0.5*h*k2));
k4 = f2((T_H2O_vektor(i) + h),(X_vektor(i) + h*k3));
X_vektor(i+1) = X_vektor(i) + h/6*(k1+2*k2+2*k3+k4);
X_2R = X_vektor(i) + h/6*(k1+2*k2+2*k3+k4);
betrag = abs(X_2R - X_2);
end
  1 个评论
Star Strider
Star Strider 2020-1-27
Is the argument to the log function here:
log((0.622+X_sat(i))/(0.622+X))
ever negative?
That is the only part of ‘f2’ I can see that could produce a complex result.

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回答（1 个）

Michael Käufl
Michael Käufl 2020-1-27
Your answer didn't solve the problem, but I found my problem because I had a look at the part you were talking of. It was a stupid parenthesis error. Thanks!

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