How to implement for-loops in Matlab Function block in Simulink

Question

I have a piece of code that works perfectly when run from the command line, but when it is run inside of a Matlab function block in my Simulink simulation, I get a matrix dimensioning error.

Using the debugger, I have figured out that the for-loop is behaving differently from how I expect and I'm not sure how to fix it without major re-writes to someone else's code.

Here is the snippet of code that is causing problems.

for k=input
        idx=4+2*(i-1)+1;
        yhat=yhat+th(idx)*cos(k.*(2.*pi.*60.*t+th(1).*t))+th(idx+1)*sin(k*(2*pi*60*t+th(1)*t));
end

Normally, k would take on each value from 2 to 13 and this would run as one would expect a for loop to run. For some reason, when I set a breakpoint on the yhat line, I am finding that k is the vector [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13], which is the transpose of what I expect input to be. Does anyone know what is going on that would make this code run differently in the Matlab Function block or how to fix it?

Hill Balliet Hill Balliet · Accepted Answer · 2019-07-16T21:22:45

facepalm, I figured it out right after posting the question. Apparently Simulink Constant blocks will output a column vector even when supplied with a row vector.

For loops iterate over the column of the supplied vector, so

for ii = [1 2; 3 4]
    ii
end

outputs [1;3] [2;4] for example. Because the constant block was supplying my input as a column vector, this led to the for loop iterating over the 1 column. Transposing the vector fixed the issue.

How to implement for-loops in Matlab Function block in Simulink

1 Answers