How to change the input of the function

I am trying to write this code, with the input of altitude (h), to give me the temp, pressure, density. I'm not sure how to make it so that i can change the value of h. The function also seems to return the same numbers when h<11000, no matter what the input number is.

function [T, P, rho] = question1 (h)

T1 = 288.15;

L = -0.0065;

R = 287;

PSL = 101325;

g = 9.81;

rhoSL = 1.225;

if h<11000

T = T1 + L*R;

P = PSL * (T/T1)^((-g)/(L*R));

rho = rhoSL * (T/T1)^(((-g)/(L*R)) +1);

else 99

end

end

[Davide Masiello]

The function returns the same values when h < 11000 because the equations in your conditional statement do not depend on h, but rather on constants.

If you could disclose your governing equations maybe a solution could be suggested.

Answer 1

[Arif Hoq]

%define your variable and call your function
T1 = 288.15;
L = -0.0065;
R = 287;
PSL = 101325;
g = 9.81;
rhoSL = 1.225;
[T, P, rho]=question1 (T1,L,R,PSL,g,rhoSL)

T = 286.2845

P = 9.7923e+04

rho = 1.1762

% your function
function [T, P, rho] = question1 (T1,L,R,PSL,g,rhoSL)
h=8000;  % change your h 
if h<=11000
    T = T1 + L*R;
    P = PSL * (T/T1)^((-g)/(L*R));
    rho = rhoSL * (T/T1)^(((-g)/(L*R)) +1);
else
T=0;
P=0;
rho=0;
end
end

[Nick Gray]

thankyou. I now get an error stating that the local function name must be different from the script name. How do I solve this?

[Arif Hoq]

maybe your function name(question1) and your matlab script name are similar. change your matlab script name other than function name.

[Walter Roberson]

Rename the script, or rename the function.

Or, since this looks like homework, quite possibly intended for a grading system, split off the part before the function definition into its own file, and run that file when you want to test your function. The grading system would then proceed to call your function with whatever parameters it wanted to test out your function.

[Arif Hoq]

See the result now. I have changed the value of h, so result also changed.

in additon, i have defined an anynomous value of conditional else . so please define your conditional else value according to your calculation.

%define your variable and call your function
T1 = 288.15;
L = -0.0065;
R = 287;
PSL = 101325;
g = 9.81;
rhoSL = 1.225;
[T, P, rho]=question1 (T1,L,R,PSL,g,rhoSL)

T = 0

P = 0

rho = 0

% your function
function [T, P, rho] = question1 (T1,L,R,PSL,g,rhoSL)
h=12000;  % change your h 
if h<=11000
    T = T1 + L*R;
    P = PSL * (T/T1)^((-g)/(L*R));
    rho = rhoSL * (T/T1)^(((-g)/(L*R)) +1);
else
T=0;
P=0;
rho=0;
end
end

[Sam Chak]

@Arif Hoq @Nick Gray

I remember my Aeronautics Professor showed me that the pressure P and density ρ of the air changes with altitude, h. Perhaps these formulas are helpful in the MATLAB code.

https://en.wikipedia.org/wiki/Barometric_formula

Then from the Ideal Gas Law, we can compute the Temperature at which pressure is calculated.