Why do I get the error saying I did not assign values to a call? I did assign my values after getting them from a function though? Anyone able to help me out and explain?

Question

Rachel Ong 2022-3-5

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https://ww2.mathworks.cn/matlabcentral/answers/1664289-why-do-i-get-the-error-saying-i-did-not-assign-values-to-a-call-i-did-assign-my-values-after-gettin

评论： Rachel Ong 2022-3-6

I got the script as attached below. I did assign T P rho and speedsound after getting it from the loop but I am getting the error:

Output argument "P" (and maybe others) not assigned during call to "atmosplots>atmos".

Error in atmosplots (line 14)

[T, P, rho, speedsound] = atmos(h)

%% Atmos function to plot the graphs of T P rho and speedsound for every altitude in ISA Atmosphere 
% Calculating T, p ,rho and speedsound for every altitude in the ISA atmosphere
% ------ Range of Altitude ------ %
hlist = linspace(0,20000,2000)
% ------ Array for storing ------ %
% 1: Altitude   2. Temperature   3. Pressure   4. Density   5. Speedsound
plotting_table = zeros(length(hlist),5);
for i=1:length(hlist)
    h = hlist(i);
    [T, P, rho, speedsound] = atmos(h)
    
    plotting_table(i,1) = hlist(i)
    plotting_table(i,2) = T
    plotting_table(i,3) = P
    plotting_table(i,4) = rho
    plotting_table(i,5) = speedsound
    
end
    
% ------ Plotting graph (X vs Y)------ %
figure % Plot for whole range of altitude
subplot(2,2,1)      % T vs Altitude
plot(plotting_table(:,2), hlist)
title('Temperature variation with altitude')
xlabel('Temperature [K]')
ylabel('Altitude [m]')
grid on
hold on 
subplot(2,2,2)      % P vs Altitude
plot(plotting_table(:,3), hlist)
title('Pressure variation with altitude')
xlabel('Pressure [Pa]')
ylabel('Altitude [m]')
grid on
hold on 
subplot(2,2,3)      % Rho vs Altitude
plot(plotting_table(:,4), hlist)
title('Density variation with altitude')
xlabel('Density [kg/m^3]')
ylabel('Altitude [m]')
grid on
hold on 
subplot(2,2,4)      % Speedsound vs Altitude
plot(plotting_table(:,5), hlist)
title('Speed of sound variation with altitude')
xlabel('Velocity [m/s]')
ylabel('Altitude [m]')
grid on
%% ------ Atmos function ------ %%
% Altitude in m
% T in kelvins
% P in pascals
% rho in kg/m^3
% Speedsound in m/s
function [T, P, rho, speedsound] = atmos(h)
h1 = 11000;    % Height of tropopause
h2 = 20000;    % End height of table
g = 9.81;
R = 287; 
c = 6.51e-3;       % temperature lapse dt/dh = - c = -6.51 degcelcius/km
T0 = 15+273.15;       % Temperature sea level
p0 = 101325;       % pressure sealevel
rho0 = 101325/R/T0;      % density sealevel = pressure / R*T, R=287, T = 15 degcelcius       
T1 = T0 - c*h1;    % Temperature at 11km
p1 = p0 * (T1/T0)^5.2506;   % Pressure at 11km
rho1 = rho0 * (T1/T0)^4.2506;   % Density at 11km
T2 = T1;    % Temperature at 20km
p2 = p1 * exp(-g/(R*T2)*(h2-h1));  % Pressure at 20km
rho2 = rho1 * exp(-g/(R*T2)*(h2-h1));  % Density at 20km
if h <= h1
%       disp('Troposphere');
    T = T0 - c*h;
    p = p0 * (T/T0)^5.2506;
    rho = rho0 * (T/T0)^4.2506;
    speedsound = (1.4*R*T)^0.5;
elseif h <= h2
%       disp('Tropopause');
    T = T1;
    p = p1 * exp(-g/(R*T)*(h-h1));
    rho = rho1 * exp(-g/(R*T)*(h-h1));
    speedsound = (1.4*R*T)^0.5;
end
return 
end

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Answer 1

Steven Lord 2022-3-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1664289-why-do-i-get-the-error-saying-i-did-not-assign-values-to-a-call-i-did-assign-my-values-after-gettin#answer_910634

You've defined your atmos function to return the value of its local variable P as the second output.

What value should be returned as that second output if not all elements of h are less than or equal to h1 and not all elements of h are less than or equal to h2? What value does your code assign to the local variable P with in that scenario? Does the local variable P even exist in that scenario?

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Rachel Ong 2022-3-6

I didnt realise this, thanks for help! I've set the range of h so it should not give me an error in those scenarios you mentioned. Thank you once again.

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