Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

I'm struggling with this problem, and don't know how to fix it, please help :)

I'm programing the PRSV ecuation of state for a multicomponent system.

I tried with the command [z]= prsv(800,1000*1000,[647.1 512.6],[22055*1000 8097*1000],[0.345 0.564],[-0.06635 -0.16816],[0.5 0.5],0) and that error shows up, i know it has something to do with the matrix size but dont know what specifically.

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

nrosust=length(Tc);
R=8.314772;

for i=1:nrosust
    k0(i)=0.378893+1.4897153*w-0.17131848*w.^2+0.0196554*w.^3;
    k(i)=k0(i)+k1*(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*(1-kij(i,j)); 
        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);

Answer 1

[the cyclist]

In this line:

k0(i)=0.378893+1.4897153*w-0.17131848*w.^2+0.0196554*w.^3;

w is a 2-element vector, and you are trying to assign it to a single element of k0.

[Bruce Lich]

Thanks! I changed it to this, and now it does work:

 k0(i)=0.378893+1.4897153*w(i)-0.17131848*w(i).^2+0.0196554*w(i).^3;