Frequency sweap euler's model

Hello,

I am trying to solve a differential equation using the euler's model:

for ii=1:length(t)-1
    du = M*a(ii) + C;
    u(ii+1) = u(ii) + du*dt; 
end

Where u and a are vectors with the same length of the time vector (defined in my code) and dt is the timestep.

Particularly, a(ii) is defined as a sinusoidal function as following:

a = sin(w*t)

I would like to make the frequency vary so I have made a linspace vector for w:

w = linspace(0, 100, 100)

therefore, mu final code is made of 2 loops:

for j=1:lentgh(w)
    for ii=1:length(t)-1
        
        du(j) = M*a(j,ii) + C;
        u(j,ii+1) = u(j,ii) + du(j)*dt; 
        
    end
end

I am obviously here because my code gives some errors. How can I fix the code? Do you have other suggestions in order to make a frequency sweap run (with differential equations involved)?