Only one graph appear instead of two.

Hello, so I'm trying to plot a graph using Antoine equation. I was given two equation and was tasked to plot a graph. Unfortunately, when I run the code, only 1 graph appear instead of 2 and I don't know where I go wrong. Help is greatly appreciated. Thank you.

Below is the code I use as reference.

A1=14.895;
B1=-3412.1;
C1=-22.627;
A2=14.751;
B2=-3331.7;
C2=-45.55;
D=30:75; %temperature range required
T=D+273; %converted to Kelvin

log10P=A1-B1./(T+C1);  %Antoine's equation
Psat1 = 10.^log10P;  %Computing Psat1

log10P=A2-B2./(T+C2);  %Antoine's equation
Psat2 = 10.^log10P;  %Computing Psat2

plot(D,Psat1,D,Psat2,'.-');
xlabel('Temperature [K]');
ylabel('Pressure [kPa]');
title('Saturation Pressure from Antoine Equation');
plot(T,Psat1,'r');
plot(T,Psat2,'b');
legend('Psat1', 'Psat2')
grid on;

Answer 1

[Star Strider]

Use the hold function —

A1=14.895;
B1=-3412.1;
C1=-22.627;
A2=14.751;
B2=-3331.7;
C2=-45.55;
D=30:75; %temperature range required
T=D+273; %converted to Kelvin

log10P=A1-B1./(T+C1);  %Antoine's equation
Psat1 = 10.^log10P;  %Computing Psat1

log10P=A2-B2./(T+C2);  %Antoine's equation
Psat2 = 10.^log10P;  %Computing Psat2

figure
plot(D,Psat1,D,Psat2,'.-')
hold on                                                         % <— ADDED
xlabel('Temperature [K]');
ylabel('Pressure [kPa]');
title('Saturation Pressure from Antoine Equation');
plot(T,Psat1,'r')
plot(T,Psat2,'b')
hold off                                                        % <— ADDED
legend('Psat1', 'Psat2', 'Location','best')
grid on;

.

Answer 2

[dpb]

You forgot

hold on

to put more on the same axes after the first...

plot(T,Psat1,'r');
hold on
plot(T,Psat2,'b');
title('Saturation Pressure from Antoine Equation');
...

will do the deed -- as will for somewhat more compact code

plot(T,Psat1,'r-',T,Psat2,'b-');

without the need for hold on. Or,

...
D=(30:75).';        % make the independent variable a column vector so results will be, too...
...
hL=plot(T,[Psat1,Psat2]);    % use plot() by column inbuilt feature, save line handles
...

For the last, the typical default line colors start with 'r', 'b' so you'll get those by default if that default order hasn't been redefined. It it has, that's the reason saved the line handles; the final step would be

set(hL,{'Color'},{'r';'B'}) % set colors explicitly

All the various syntax options are in the doc for plot; it's far more flexible than simply "one-at-a-time" use.