NaN generated as output

Hello

I've an function which calculates the dew point pressure. When i call it to generate the outputs such a x(the composition in the liquid phase) and Pressure. It produces output with no values and content of 'NaN'.

If i run the function, segment by segment to see where the error might lie. I think i've narrowed it down to a loop. This is stated below:

iter=0
while max(abs((PD*z-Ps.*x.*gamma)./(PD*z)))>0.001 && iter<100
    PD=1/sum(z./Ps.*gamma);
    x=(PD*z)./(Ps.*gamma);
    [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,x);
    iter=iter+1;
end

Though it is possible the issue lies elsewhere. The function is stated below:

function [PD,x]=PD_VLE_WILSON(C,MW,rhoL,BIP,T,z)
c=length(z);
for i=1:c
    Ps(i)=exp(C(i,1)+C(i,2)/T+C(i,3).*log(T)+C(i,4).*(T).^(C(i,5)));
end
[PD,x]=PD_VLE_ID(C,T,z);
[gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,x);
iter=0
while max(abs((PD*z-Ps.*x.*gamma)./(PD*z)))>0.001 && iter<100
    PD=1/sum(z./Ps.*gamma);
    x=(PD*z)./(Ps.*gamma);
    [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,x);
    iter=iter+1;
end
if iter<1000
    PD=1/sum(z./Ps.*gamma);
    x=(PD*z)./(Ps.*gamma);
else
    PD=0;
    x=0;
end
end

The first subprogram:

function [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,x)
%This program calculates the activity coefficients (gamma) and the 
%activities (a) of each component of a mixture of c components using the 
%Wilson model. 
%INPUT PARAMETERS: MW: vector (1xc) reporting the molecular weights of the 
%c components; rhoL, vector (1xc) reporting the liquid density of the c 
%pure components at temperature T; BIP is a matrix cxc reporting the energy   
%interaction parameters (BIP(i,j)=lambda_ij-lambda_ii, J/mol). The energy
%interaction parameters are temperature independent; T: temperature of the 
%system; x vector (1xc) reporting the mole fractions of the components of 
%the mixture.   
%OUTPUT PARAMETERS: gamma: vector 1xc reporting the activity 
%coefficients of the components of the mixture; a: vector 1xc reporting the 
%activities of the components of the mixture. 
%Unless otherwise stated, all input/output parameters are expressed
%according to MKS.
R=8.314;
c=length(x);
%Molar volumes of the pure liquid components composing the mixture
VL=1./((rhoL*1000)./MW);
%Lambda terms (dimensionless) of the Wilson formula
for i=1:c
    for j=1:c
        Lambda(i,j)=(VL(j)/VL(i))*exp(-BIP(i,j)/(R*T));
    end
end
for i=1:c
    for j=1:c
        A=sum(x.*Lambda(j,:));
        C(j)=x(j)*Lambda(j,i)/A;
    end
    lngamma(i)=1-log(sum(x.*Lambda(i,:)))-sum(C);
    gamma(i)=exp(lngamma(i));
    a(i)=gamma(i)*x(i);
end
end

The second subprogram.

function [PD,x]=PD_VLE_ID(C,T,z)
c=length(z);
for i=1:c
    Ps(i)=exp(C(i,1)+C(i,2)/T+C(i,3).*log(T)+C(i,4).*(T).^(C(i,5)));
end
PD=1/sum(z./Ps);
x=(PD*z)./Ps;
end

And my input if you need to run it:

T=343;
z=[0.1 0.9];
P=4000000;
MW=[46 18];
rhoL=[789 997];
BIP=[1972.2	3700.10;1972.2	3700.10];
C1=[73.649	74.475];
C2=[7258.2	-7164.3];
C3=[-7.3037	-7.327];
C4=[4.17E-06 3.13E-06];
C5=[2  2];
C = [C1' C2' C3' C4' C5'];

[Stephen23]

@Gamas Gamose: what is your question? You forgot to ask us anything.

[N/A]

The question is; Why does it generate NaN instead of giving me real values.

I expected to get x-vales between 0-1 and High pressure values.

Answer 1

[Steven Lord]

Set an error breakpoint to force MATLAB to enter debug mode as soon as a NaN or Inf value is generated. Then you can see the exact line that generated the NaN or Inf value and examine the values of your variables at that point. If you need to see with what values your function was called you can work your way up the function call stack using the techniques in the first section on this documentation page.