Index exceeds the number of array elements (1).

Im struggling with this code, the problem occurs in line 40

lnphi=-log(z-B)+(b(i)*(z-1)/b)-((A/(2*sqrt(2)*B))*((2*sum_A(i)/sum_a)-(b(i)/b))*log((z+(1+sqrt(2)*B))/(z+(1-sqrt(2)*B))));

Here's the full code, im trying to program the PRSV ecuation of state. Please help :)

function[phi]= prsv(T,P,Tc,Pc,w,k1,x)

nrosust=length(Tc);
R=8.314772;

for i=1:nrosust
    k0(i)=0.378893+1.4897153*w(i)-0.17131848*w(i).^2+0.0196554*w(i).^3;
    k(i)=k0(i)+k1(i)*(1+(T/Tc(i))^0.5)*(0.7-(T/Tc(i)));
    alpha(i)=(1+k(i)*(1-((T/Tc(i))^0.5)))^2;
    a(i)=(0.457235*(R^2*Tc(i).^2/Pc(i)))*alpha(i);
    b(i)=0.07779607*(R*Tc(i)/Pc(i)); 
end

sum_a=0;

for i=1:nrosust
    for j=1:nrosust
        aij(i,j)=(a(i)*a(j))^0.5;
        sum_a=sum_a+x(i)*x(j)*aij(i,j);
    end    
end

b=sum(x.*b);

A=sum_a*P/(R*T)^2;
B=b*P/(R*T);

Pol=[1 -1+B A-3*B^2-2*B -A*B+B^2+B^3];
Z=roots(Pol);
z=max(Z);

for i=1:nrosust
    sum_A(i)=0;
    for j=1:nrosust
        sum_A(i)=sum_A(i)+x(j)*aij(i,j);
    end
end

for i=1:nrosust
    lnphi=-log(z-B)+(b(i)*(z-1)/b)-((A/(2*sqrt(2)*B))*((2*sum_A(i)/sum_a)-(b(i)/b))*log((z+(1+sqrt(2)*B))/(z+(1-sqrt(2)*B))));
    phi(i)=exp(lnphi);
end    

[per isakson]

>> prsv(1,2,3,4,5,6,7)
ans =
    0.0085916 +  0.0013123i

What input data did you use to get this error?

[Bruce Lich]

Hi! When every input is a scalar, it works just fine. The problem is when i try it with vectors as inputs (for mixes).

i.e. this one:

(note that T and P are global parameters, they are always scalars, whilst the rest are not unless its a pure substance)

[phi]= prsv(800,1000*1000,[647.1 512.6],[22055*1000 8097*1000],[0.345 0.564],[-0.06635 -0.16816],[0.3 0.7])

Answer 1

[per isakson]

Here are some links on debugging in Matlab

• Debug a MATLAB Program
• Debugging in MATLAB
• Debugging session
• Debugging Approaches