code correction : subplot in for + length problem

Hello, I was wondering if it was possible to write the code with subplots as I did. The idea of the program is to display a low-pass filter on the same window, with the index response at the top and the frequency response at the bottom. We vary N and display the curves in different colors on the same graph (the same subplot), whether for RF or stem.

Added to this is an error during program execution :

Error using stem (line 43)

X must be same length as Y.

Error in filtrage (line 11)

stem(axe,formula);

But when I test the length with length I get the same size. I'll let you be the judge:

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% Passe-Bas
figure 
for N = [10,40,100]
    subplot(2,1,1);
    axe,formula = passe_bas(N);  
    stem(axe,formula);
    
    subplot(2,1,2); 
    RF = abs(freqz(formula));
    f = linspace(0,0.5,length(RF)); 
    plot(f,RF);
end

Unrecognized function or variable 'axe'.

function [axe,formula] = passe_bas(N)
v0 = 0.2; 
n=-round(N/2):1:round(N/2);
axe = 0:1:length(n)-1;

formula=2*v0*sinc(2*v0*n);

end

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Thanks for your answers.

Answer 1

[Chunru]

figure 
for N = [10,40,100]
    subplot(2,1,1);
    hold on
    [axe,formula] = passe_bas(N); 
    % brackets above
    stem(axe,formula);
    
    subplot(2,1,2);   
    hold on
    RF = abs(freqz(formula));
    f = linspace(0,0.5,length(RF)); 
    plot(f,RF);
end

 
 
function [axe,formula] = passe_bas(N)
    v0 = 0.2; 
    n=-round(N/2):1:round(N/2);
    axe = 0:1:length(n)-1;
    
    formula=2*v0*sinc(2*v0*n);
    
end