How get this program to calculate derivative properly?

function [Yn]=Jaroslaw_Dabrowski(dt, N)
% Help funkcji [Yn]=Jaroslaw_Dabrowski(dt, N)
%funkcja obliczna pochodne n-tego stopnia i rysuje ich wykres.
%Zmienne wejściowe:   dt - odstępy czasowe,
%                     N  - stopień pochodnej.
%Zmienne wyjściowe:   Yn - obliczona pochodna.
A=2;
w=1;
hold on
if N>10;
    error ('myApp:argChk','Decrease the number of loop iterations')
elseif N<=10;
    for i=1:N;
        t=-3*pi:dt:3*pi;
        Yn=A*sin(w*t);
        Ynn=A*sin(w*(t+dt));
        Yn(189)=Ynn(188);
        size(t);
        size(Yn);

        dYn=diff(Yn,i)./dt;
        size(t);
        dYn(189)=dYn(1);
        size(dYn);
        subplot(5,2,i)
        grid on
        plot(t,dYn)
        xlabel('Time')
        ylabel('Amplitude')
        legend(strcat('Y_n, n=',num2str(i)))
    end
end
        
end

[darova]

Can you be more specific? What is wrong?

Show the original curve and the curve you want to see. Show the curve derivative was taken from.

[Jaroslaw Dabrowski]

Sorry, i missed answer. Could you check the answer below?

[darova]

No matter how much you take derivative cos() will be always the same frequency

So your function does return correct output

Answer 1

[KSSV]

Yn=A*sin(w*t);
dYn = A*w*cos(w*t) ; 

[KSSV]

Replace:

dYn=diff(Yn,i)./dt;

with:

dYn=diff(Yn)./dt;

[Jaroslaw Dabrowski]

It won't work like that. i must be there, becouse each plot must be in higher derivative.

Answer 2

[Jaroslaw Dabrowski]

It should be like that. Theoretically derivative is wrong in my code, and i have no idea how to correct it