hello
I finally plotted 3 figures as it was not clear to me is you wanted to use P or pPR as the pressure value . Anyway, I wanted to see the difference between the two =>see first plot
aslo I would suggest to put your data in a separate txt file so you get much more compact and nicer code
so in brief , a very simple suggestion below
your data are now in the attached txt file
%% Data
M = readmatrix('mydata.txt',"NumHeaderLines",1);
%% Data extraction
T = M(:,1); % extract Temperature data
P = M(:,2); % extract Pressure data
rho = M(:,3); % extract Density data
[T, I] = sort(T); % sorted Temperature [K]
P = P(I); % sorted Pressure [MPa]
rho = rho(I); % sorted Density [kg/m³]
v = 1./rho; % specific volume [m³/kg]
%% Parameters
R = 8.314462618/(120.02e-3)*1e-6; % Gas constant [MJ/(kg*K)]
Tc = 339.45; % Critical Temperature [K]
Pc = 3642.77e-3; % Critical Pressure [MPa]
omega = 0.2986;
kappa = 0.37464 + 1.54266*omega - 0.26992*omega^2;
alpha = (1 + kappa*(1 - sqrt(T/Tc))).^2;
a = 0.45724*(R^2*Tc^2)/Pc; % parameter a in P–R EoS (Wiki)
% b = 0.07780*(R^2*Tc^2)/Pc; % parameter b (defined by OP)
b = 0.07780*(R*Tc)/Pc; % parameter b in P–R EoS (Wiki)
%% Peng–Robinson equation of state
pPR = (R*T)./(v - b) - (a*alpha)./(v.^2 + 2*b*v - b^2);
%% Graphing
% Two figures in to two plots.
% I need to plot (the density Vs pressure) and ( the density vs. Temperature)
% for the data itself and using Peng Robinson model.
%plot (pPR Vs P)
figure(1)
plot(P,pPR,'*');
title('pPR Vs P');
xlabel('P [MPa]');
ylabel('pPR [MPa]');
%plot (density Vs pressure pPR)
figure(2)
plot(pPR,rho,'*');
title('Density Vs Pressure');
xlabel('pressure [MPa]');
ylabel('density [kg/m³]');
%plot (density Vs Temperature)
figure(3)
plot(T,rho,'*');
title('Density Vs Temperature');
xlabel('temperature [K]');
ylabel('density [kg/m³]');
