MATLAB function gives me error

Hello,

As you can see from the photo I attached, I am trying to run a simulink model that uses MUX blocks, Matlab function block, and integrator in a feedback loop.

The code in the Matlab function is:

function y = fcn(u)
vta = u(1); vtb = u(2); vtc = u(3);
ea = u(4); eb = u(5); ec = u(6);
ia = u(7); ib = u(8); ic = u(9);
iLa = u(10); iLb = u(11); iLc = u(12);
R = 0.02; L = 0.04; RL = 3; LL = 0.01; C = 0.001;
de = (1/C)*[ia-iLa;ib-iLb;ic-iLc];
di = (1/L)*[vta-ea-R*ia; vtb-eb-R*ib; vtc-ec-R*ic];
diL = (1/LL)*[ea-RL*iLa; eb-RL*iLb; ec-RL*iLc];
y = [de;di;diL];

And the error is:

Could you please help me how to troubleshoot it? I think the issue has to do with the feedback loop but I don't know how to fix it.

Thank you

Answer 1

[Simon Chan]

Check the length of variable 'u'.

Looks like there is only 1 element inside variable 'u', but the function request to find the elements from #1 to #12 from 'u'.

Or could you post what is the content of 'u'?

[Milad Shojaee]

Thank you for the response

Variable 'u' should have 12 elements. 3 from the previous stage and 9 from the feedback loop. But I don't know why it only generates 1 element in its output. Based on "y = [de;di;diL]", it should generate a vector with 9 elements because de, di, and diL has 3 elements each.

It seems that generation of those elements in fcn output deponds on its inputs but the inputs are also dependent on the output elements!

[Simon Chan]

So you need to think about to assign some initial values for those 9 elements before feeding into this function.

After you combine 3 elements obtained from the previous stage and 9 dummy feedback elements. The function should work properly.

[Milad Shojaee]

I added initial conditions and it worked. Thank you!

Answer 2

[Walter Roberson]

Those solid markings appear to me to indicate that you are using a Simulink Bus Creator https://www.mathworks.com/help/simulink/slref/buscreator.html

If you were concatenating the elements into a vector, you would see hollow white blocks instead of filled blocks; see https://www.mathworks.com/help/simulink/slref/vectorconcatenate.html

You can either switch to using vector concatenate and have the signal be a vector, or before you send the bus into the function block you can convert to vector; https://www.mathworks.com/help/simulink/slref/bustovector.html

[Milad Shojaee]

Thank you for your reply. I replaced the Bus Creator with Vector concatenate block but it did not make any difference. I still had the same issue. However, as Simon suggested, I added initial conditions to the feedback loop and it worked.