Failure in initial objective function evaluation. FSOLVE cannot continue.

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Andrew
Andrew 2019-4-19
评论： Andrew 2019-4-19
Right after the second while loop in the code below, I am calling fsolve on a function that solves for 5 unknowns. I keep getting the error "Failure in initial objective function evaluation. FSOLVE cannot continue." I have looked at several other posts with this issue, but wasn't able to figure out what is wrong with my code. I also have another code that is very similar to this one and works just fine.
p1 = 0.01; %atm (pressure @ 1)
T1 = 200; %K (temp @ 1)
u1 = 500; %m/s (speed @ 1)
n_N2 = 0.79; %mols
n_O2 = 0.21; %mols
M_N2 = 28.014; %kg/kmol
M_O2 = 31.998; %kg/kmol
M_N = 14.007; %kg/kmol
M_O = 15.999; %kg/kmol
M_NO = 30.006; %kg/kmol
R = 8.314459848; %kJ/K*kmol
rho1 = p1*(n_N2*M_N2 + n_O2*M_O2)/((n_N2 + n_O2)*R*T1);
h1 = n_N2*cp_n2(T1)*T1 + n_O2*cp_o2(T1)*T1;
rho2_g = rho1/0.1;
counter = 0;
error = 1.0;
x0 = [0.1, 0.1, 0.1, 0.1, 0.1];
while error > 0.0001 || counter <= 10000
p2 = p1 + rho1*u1^2*(1 - rho1/rho2_g);
h2 = h1 + (u1^2/2.0)*(1 - (rho1/rho2_g)^2);
T2_g = 300.00;
err = 1.0;
count = 0;
while err < 0.001 || count <=10000
X = fsolve(@(x)Xi_eflow(x, p2, T2_g), x0);
h2_g = X(1)*cp_n2(T2_g)*T2_g + X(2)*cp_o2(T2_g)*T2_g + ...
X(3)*cp_o(T2_g)*T2_g + X(4)*cp_n(T2_g)*T2_g + ...
X(5)*cp_no(T2_g)*T2_g;
err = abs(h2 - h2_g);
if err > 0.0001
T2_g = (T2 + T2_g)/2.0;
end
if count == 10000
z = count
end
end
rho2 = p2*(Xn2*M_N2 + Xo2*M_O2 + Xn*M_N + Xo*M_O + Xno*M_NO)...
/((Xn2 + Xo2 + Xn + Xo + Xno)*R*T2_g);
if error > 0.001
rho2_g = (rho2_g + rho2)/2
end
if counter == 10000
y = counter
end
end
Below is the function that fsolve is used on.
function F = Xi_eflow(x, P, T)
R = 8.314459848; %kJ/kmol*K
Xn2 = x(1);
Xo2 = x(2);
Xo = x(3);
Xn = x(4);
Xno = x(5);
Go = -1.011066E-17*T^6 + 1.816726E-13*T^5 - 1.317613E-9*T^4 + ...
4.993102E-6*T^3 - 1.081611E-2*T^2 - 53.86166*T + 248642;
Gn = -9.090730E-18*T^6 + 1.667190E-13*T^5 - 1.243770E-9*T^4 + ...
4.874266E-6*T^3 - 1.115735E-2*T^2 - 52.39920*T + 471978.9;
Gno = 2*(7.363399E-20*T^6 - 1.268925E-15*T^5 + 3.387909E-12*T^4 + ...
5.794901E-8*T^3 - 2.905865E-4*T^2 - 12.27637*T + 90286.60);
F(1) = Xn2 + Xo2 + Xo + XN + Xno - 1;
F(2) = (2*Xn2 + Xn + Xno)/(2*Xo2 + Xo + Xno) - (0.79/0.23);
F(3) = exp(-Go/(R*T)) - Xo*P^(0.5)/Xo2^(0.5);
F(4) = exp(-Gn/(R*T)) - Xn*P^(0.5)/Xn2^(0.5);
F(5) = exp(-Gno/(R*T)) - Xno^2/(Xn2*Xo2);
end
Any help is appreciated. Thank you!
Edit: Forgot to put some other functions on here.
function y = cp_n(x)
y = 9.982621E-22*x^6 - 1.872004E-17*x^5 + 1.321452E-13*x^4 - ...
3.827231E-10*x^3 + 4.821461E-7*x^2 - 2.469692E-4*x + 20.82571;
end
function y = cp_n2(x)
y = 2.693757E-20*x^6 - 4.651184E-16*x^5 + 3.103549E-12*x^4 - ...
9.831534E-9*x^3 + 1.383600E-5*x^2 - 2.998751E-3*x + 28.88362;
end
function y = cp_no(x)
y = 2.489814E-20*x^6 - 4.154027E-16*x^5 + 2.638902E-12*x^4 - ...
7.714111E-9*x^3 + 9.019032E-6*x^2 + 1.658686E-3*x + 28.56333;
end
function y = cp_o(x)
y = 1.232504E-20*x^6 - 2.139706E-16*x^5 + 1.462356E-12*x^4 - ...
4.982123E-9*x^3 + 8.915414E-6*x^2 - 7.957834E-3*x + 23.62581;
end
function y = cp_o2(x)
y = 9.818398E-22*x^6 + 1.336256E-17*x^5 - 3.741595E-13*x^4 + ...
2.662210E-9*x^3 - 8.689588E-6*x^2 + 1.570265E-2*x + 25.37744;
end
  2 个评论
Matt J
Matt J 2019-4-19
Here's what I get when I run your code,
Undefined function or variable 'cp_n2'.
Error in test (line 13)
h1 = n_N2*cp_n2(T1)*T1 + n_O2*cp_o2(T1)*T1;
Andrew
Andrew 2019-4-19
Sorry, I forgot to give the functions for my cp values. I have added them above. Sorry about that.

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采纳的回答

Matt J
Matt J 2019-4-19
Instead of XN, in this line
F(1) = Xn2 + Xo2 + Xo + XN + Xno - 1;
should it be Xn?

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