Error: Contour endpoints and waypoints must be finite.

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')

Answer 1

[Sean de Wolski]

It looks like it's complaining about this line:

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

For more information.

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.

[Steven]

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]

So it's exactly where I predicted it would be. Don't use Inf as xmin.