How do I avoid hardcoding output size when using simulink coder.extrinsic?

I have a matlab function 'control_fun' that I'm using in a simulink model. It does not compile with codegen so I'm using coder.extrinsic to run the model. The problem is that I have to hardcode the size of the output of controlfun when I would like this to be parameter that can change (not during a simulation, but between simulations). I use a simulink matlab-function to call the control_fun.

This works:

function u = call_control_fun(data, parameter)  % parameter = 5

coder.extrinsic('control_fun')
u = zeros(5,1);
u = control_fun(data)

But this doesn't:

function u = call_control_fun(data, parameter)  % parameter = 5

coder.extrinsic('control_fun')
u = zeros(parameter, 1);
u = control_fun(data)

This results in an error:

Block ''call_controlfun'' does not fully set the dimensions of output 'u'.

I have tried playing with coder.varsize but haven't gotten anything to work.

[Josiah Wai]

update: an okay-ish workaround is to use a large fixed output size with zero-padding, then elsewhere in the model use variables to index into u and remove the zero-padding.

Answer 1

[Fangjun Jiang]

I suspect that the "parameter" in your code is not really a parameter-by-definition by the MATLAB Function block. It appears as an Inport to the MATLAB Function block, does it?

In MATLAB Function block editor, click "Edit Data", change the "Scope" or "Type" of "parameter" from "Input" to "Parameter". Then, "parameter" won't appear as an Inport to the MATLAB Function block, it becomes a parameter of the block, just like any other parameters of any other Simulink blocks. You set its value in base workspace or model workspace. Then the error you had should disappear.

[Josiah Wai]

Thank you, it was set as a parameter but the workaround is okay for now.