Plotting a multivariable function

Hi, I have a multivariable function as you can see down below. The function works perfect but I have a problem. I need to plot v_cal - v_true when a_ft is equal to 28000. However, when I tried to run the function, MATLAB asks me for v_cal and a_ft values. When I input these values, it plots the v_cal-v_true graph as a constant function. How can I fix this? Thanks in advance.

function v_true=CaltoTrue(a_ft,v_cal)

a=a_ft*0.3048;
b=-0.0065;
R=287.05287;
gr_0=9.80665;
p0=101325;
T0=288.15;

pr=p0*((T0+b*a)/T0)^(-gr_0/(b*R));
T=T0+b*a;
ad=pr/(R*T);

k=1.4;
nu=(k-1)/k;
ad_0=1.225;

v_true=(((((1+(nu*ad_0*(v_cal)^2)/(2*p0))^(1/nu)-1)*p0/pr+1)^nu-1)*(2*pr)/(nu*ad))^(1/2);

if a_ft==28000
    v_cal=0:500;
    fplot(v_true)
    xlabel('V_Cal')
    ylabel('V_True')
end


end

Answer 1

[KALYAN ACHARJYA]

a_ft=28000;
v_cal=0:500;
CaltoTrue(a_ft,v_cal)

ans = 1×501

0 1.5762 3.1524 4.7285 6.3046 7.8806 9.4565 11.0323 12.6079 14.1833 15.7586 17.3336 18.9084 20.4830 22.0573 23.6312 25.2049 26.7782 28.3512 29.9238 31.4960 33.0678 34.6391 36.2100 37.7804 39.3503 40.9197 42.4885 44.0568 45.6245

function v_true=CaltoTrue(a_ft,v_cal)
a=a_ft*0.3048;
b=-0.0065;
R=287.05287;
gr_0=9.80665;
p0=101325;
T0=288.15;
pr=p0*((T0+b*a)/T0)^(-gr_0/(b*R));
T=T0+b*a;
ad=pr/(R*T);
k=1.4;
nu=(k-1)/k;
ad_0=1.225;
temp=nu*ad_0.*(v_cal).^2;
temp2=(1+temp/(2*p0)).^(1/nu)-1;
v_true=(((temp2.*p0/pr+1).^(nu)-1).*(2*pr)/(nu*ad)).^(1/2);
plot(v_true)
grid on; 
xlabel('V_Cal')
ylabel('V_True')
end 

#Not costant, there is a slight variation, please check the equation, it is more about digging those equations rather than matlab code.

[Sazcl]

a_ft=28000;
v_cal=0:500;
CaltoTrue(a_ft,v_cal)

ans = 1×501

0 1.5762 3.1524 4.7285 6.3046 7.8806 9.4565 11.0323 12.6079 14.1833 15.7586 17.3336 18.9084 20.4830 22.0573 23.6312 25.2049 26.7782 28.3512 29.9238 31.4960 33.0678 34.6391 36.2100 37.7804 39.3503 40.9197 42.4885 44.0568 45.6245

function v_true=CaltoTrue(a_ft,v_cal)
a=a_ft*0.3048;
b=-0.0065;
R=287.05287;
gr_0=9.80665;
p0=101325;
T0=288.15;
pr=p0*((T0+b*a)/T0)^(-gr_0/(b*R));
T=T0+b*a;
ad=pr/(R*T);
k=1.4;
nu=(k-1)/k;
ad_0=1.225;
temp=nu*ad_0.*(v_cal).^2;
temp2=(1+temp/(2*p0)).^(1/nu)-1;
v_true=(((temp2.*p0/pr+1).^(nu)-1).*(2*pr)/(nu*ad)).^(1/2);
plot(v_true)
grid on; 
xlabel('V_Cal')
ylabel('V_True')
end 

Thanks a lot, but I don't understand where exactly you wrote the first three lines of code. When I place it above the function, I get this error: Local function name must be different from the script name.

[KALYAN ACHARJYA]

#Your Comment: Edited: TTo run the code here itself (Tap Green Tringular Button-Online) or try it on Matlab Platform (System-Offline)