# Error: Contour endpoints and waypoints must be finite.

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Steven il 6 Dic 2012
I'm trying to write a function to plot the Cp of a compound, and I keep getting this error when I try to intergrate. I'm using the 2012 version of matlab.
function outputValue=Cps()
Pc=4550;
Tc=654;
b = .092968;
w = .22894;
k = 0.37464 + 1.54226*w - 0.26992*w^2;
R = 8.314;
Ai = 112.057;
Bi = -0.8324;
Ci = 0.002865;
Di = -0.000003;
v = [];
T = [300:1:1000];
Cp = [];
Cpi = [];
Cv = [];
dPdT = [];
dPdV = [];
alpha= []
P = [.02.*Pc .5.*Pc Pc 2.*Pc];
for s = 1:4
for t = 1:length(T)
alpha(t) = (1+k.*(1-sqrt(T(t)./Tc))).^2;
a = (.45724.*(R.*Tc).^2.*alpha(t))./Pc;
A = (a.*P(s))./(R.^2.*t.^2);
B = (P(s).*b)./(R.*t);
Z = [1 -(1-B) (A-3.*B-2.*B) -(A.*B-B.^2-B.^3)];
r =roots(Z);
for i = 1:3
if ((imag (Z(i))~=0))
Z(i)=0;
end
end
G(t) = max(r);
v(t) = (G(t).*R.*t)./P(s);
Cpi(t) = Ai + Bi.*T(t) + Ci.*T(t).^2 + Di.*T(t).^3;
C = ((k^2+k)./(2.*sqrt(Tc)));
SecondDerivative = @(x) ((a.*C.*(1/T(t).^1.5))./(x.*(x+b)+b.*(x-b)));
dPdT(t) = (R./(v(t)-b))-a.*(k.*sqrt(alpha(t)./(T(t).*Tc))./(v(t).*(v(t)+b)+b.*(v(t)-b)));
dPdV(t) = (-R.*T(t)/(v(t)-b).^2)+((2.*a.*(v(t)+b))./((v(t).*(v(t)+b)+b.*(v(t)-b))).^2);
Cv(t) = (Cpi(t)-R) + (T(t).*integral(SecondDerivative,Inf,v(t)));
Cp(t) = Cv(t) - (T(t).*v(t).*(dPdT(t)).^2)./dPdV(t);
end
end
plot(T,Cp,'-g')
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### Risposte (1)

Sean de Wolski il 6 Dic 2012
Modificato: Sean de Wolski il 6 Dic 2012
Cv(t) = (Cpi(t)-R) + (T(t).*integral(SecondDerivative,Inf,v(t)));
because it does not like the Inf as the minimum boundary, xmin! This makes sense.
doc integral
Also as an FYI, it typically pays to paste the full eror message. The error messages contain diagnostic information like line numbers and the stack that make it much easier to debug.
##### 2 CommentiMostra NessunoNascondi Nessuno
Steven il 6 Dic 2012
Error using integralCalc (line 35) Contour endpoints and waypoints must be finite.
Error in integral (line 89) Q = integralCalc(fun,a,b,opstruct);
Error in Cps (line 41) Cv(t) = (Cpi(t)-R) + (T(t).*integral(SecondDerivative,Inf,v(t)));
Does that help?
Sean de Wolski il 6 Dic 2012
So it's exactly where I predicted it would be. Don't use Inf as xmin.

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