How to get values from a struct?

Hello, I want to extract the ksi1 and ksi2 values from S structure to that I can evaluate yCO, yCO2, etc. to plot them vs Temperature. But I could not do it. I tried to use A = S.ksi1 but even though I can see every value in the command window, workshop only gives me the final value of A in sym type. So I was wandering How can I extract ksi1 and ksi2 so that I can evaluate yCO, yCO2, etc.with them. Thank you in advance.

 clc;
 clear;
 nCO = 1; %starting mol
 nCO2 = 1; %starting mol
 nH2 = 2; %starting mol
 nCH3OH = 0; %starting mol
 nH2O = 1; %starting mol
 R = 8.314;%J/molK
 deltaGrxn1 = -24.8; %kJ/mol
 deltaHrxn1 = -90.2; %kJ/mol
 deltaSrxn1 = -0.2; %(deltaGrxn1 - deltaHrxn1)/(-T)
 deltaGrxn2 = -28.6; %kJ/mol
 deltaHrxn2 = -41.2; %kJ/mol
 deltaSrxn2 = 0.042; %(deltaGrxn2 - deltaHrxn2)/(-T)
 T = 298:10:800; %Temperature Values
 for i = 1:size(T,2)
     dG1(i) = deltaHrxn1 - T(i) * deltaSrxn1;
     Ka1(i) = exp(-dG1(i)/(R*T(i)));
     dG2(i) = deltaHrxn2 - T(i) * deltaSrxn2;
     Ka2(i) = exp(-dG2(i)/(R*T(i)));
     syms ksi1 ksi2
     eqn = (((ksi1)./(1-ksi1-ksi2))./((2-2*ksi1-ksi2)/(4-2*ksi1))^2)==Ka1(i);(((1+ksi2).*(2-2*ksi1-ksi2))./((1-ksi2).*(1+ksi2)))==Ka2(i);
     S = vpasolve(eqn,ksi1,ksi2);
     
     yCO = ((1 - ksi1 - ksi2)./(4 - 2*ksi1));
     yCO2 = ((1 + ksi2)./(4 - 2*ksi1));
     yH2 = ((2 - 2*ksi1 - ksi2)./(4 - 2*ksi1));
     yCH3OH = ((ksi1)./(4-2*ksi1));
     yH2O = ((1-ksi2)./(4-2*ksi1));
 end

Answer 1

[Landan Rubenstein]

Hello,

In your code, S is always a scalar, so A = S.ksi1 should be sufficient to return the scalar value for ksi1. If instead you were recording S on each loop with

S(i) = vpasolve(eqn,ksi1,ksi2);

you could extract each of the S(i).ksi1 values into a vector with

A = [S.ksi1];

This will return a sym vector.

This works because S.x where S is a non-scalar struct returns a comma-seperated list containing the set of values of x (see https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html), and a vector is formed by enclosing a comma-seperated list with square brackets ([]).

I hope this helps.

[asli eylul sert]

Thank you!