Why is the set of numbers p2 not showing up on my graph

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dpb
dpb on 20 Sep 2024
Edited: dpb on 20 Sep 2024
Quite possible the values are nan from the looks of the equations, but since you posted as an image instead of text, it would take retyping everything over to do anything specific.
Try
figure
semilogx(h,p1)
yyaxis right
semilogx(h,p2)
and you'll see the value for p2 is quite small and goes to zero quickly.
[min(p2) max(p2)]

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Answers (1)

Alan Stevens
Alan Stevens on 21 Sep 2024
Edited: Alan Stevens on 21 Sep 2024
Should it be more like this? (Though I don't recognize the value you have for the gas constant; and temperature would normally be in K, whereas yours looks like C - perhaps 250K is appropriate for high up in the atmosphere. However, you haven't supplied the units, so it's difficult to tell!).
G0 = 9.80665;
R = 287.053; % ?
p0 = 101325;
RE = 6371000;
T = 250; % ?
h = linspace(0,100);
p1 = p0*exp(-G0*h*1000./(R*T));
p2 = p0*exp(-G0*RE*RE*h*1000./(RE + h*1000).^2/(R*T));
semilogx(p1,h,p2,h), grid
xlabel('pressure (pa)')
ylabel('altitude [km)')
legend('constant gravity','variable gravity')

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