# Execute Matlab function in Simulink

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Hello to all,

I have this Matlab function, i would like to execute in Simulink using "User-Defined->Matlab Function" from the Library.

This is the function I want to execute:

function y = moving_average2(u, Tf, Ts)

% Check if the input data is long enough

N = ceil(Tf/Ts);

if numel(u) < N

N = numel(u);

end

% Initialize the result array

y = zeros(size(u));

disp(N)

% Calculate the moving average

for i = N:numel(u)

y(i) = mean(u(i-N+1:i));

end

end

and when tested, I have called this function from the following simple script:

clear; clc; close all

t = 0:0.1:10;

u = sin(t);

Tf = 2; T = 0.1;

y = moving_average(u, Tf, T);

plot(t, u);hold on; grid on;

plot(t, y, 'r');

legend("Input", "Output");

The above script when executed produce the following result:

However, when this very same function is called from the Simulink as shown in picture:

The result is very different, as if averaging is not applied at all. Input and output signals are matching perfectly (Simulation s 10 sec, auto, fixed size (auto).

Can you please suggest what I'm doing wrong?

My guess it is because Simulink executes this function for each input sample, and that is the difference comparing with the script, so basically I would need to modife the function as it would be called in an infinite loop in cyclic manner.

Thank you!

##### 0 Comments

### Accepted Answer

Paul
on 13 Feb 2024

You are correct. In Matlab, the code looks like this (actually making the call to moving_average2)

t = 0:0.1:10;

u = sin(t);

Tf = 2; T = 0.1;

%y = moving_average(u, Tf, T);

y = moving_average2(u, Tf, T);

figure

plot(t, u);hold on; grid on;

plot(t, y, 'r');

legend("Input", "Output");

In Simulink, the implementation is essentially a loop on scalar values of u, one for each value of t (assuming the simulink step size is 0.1 for illustration). As the disp command would show (I commented it out), in Simulink it's just a one point moving average.

figure

for tval = t

u = sin(tval);

Tf = 2; T = 0.1;

%y = moving_average(u, Tf, T);

y = moving_average2(u, Tf, T);

plot(tval, u,'o');hold on; grid on;

plot(tval, y, 'or');

legend("Input", "Output");

end

Is there a reason you want to use this function in Simulink instead of just computing the moving average wtih a simplle transfer function block (though some extra work would be required if you really want the output to be zero for the first N-1 samples.

function y = moving_average2(u, Tf, Ts)

% Check if the input data is long enough

N = ceil(Tf/Ts);

if numel(u) < N

N = numel(u);

end

% Initialize the result array

y = zeros(size(u));

%disp(N)

% Calculate the moving average

for i = N:numel(u)

y(i) = mean(u(i-N+1:i));

end

end

##### 2 Comments

Paul
on 13 Feb 2024

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