Check for missing argument or incorrect argument data type in call to function 'is'. Error in optimizer (line 105) if is(u{i},'complex')

[nbahari]

Hello All,
I'm working on a fairly big toolbox and I'm using YALMiP with GUROBI. I keep facing an error whose source of error I can not narrow down to. This error has kept popping up. I kept trying to figure out what the problem could be. I wish I could be able to provide a piece of code where I assumed to be the problem source. I checked if there is any imaginary number in the inputs using the function ~isreal. There is no imaginary number in the inputs.

My question is if there are some common causes for this error. The error is:

Check for missing argument or incorrect argument data
type in call to function 'is'.

Error in optimizer (line 105)
        if is(u{i},'complex')

The whole error message I get is the following. This shows there is something wrong in the input arguments of the optimizer that I can not figure out.

Check for missing argument or incorrect argument data
type in call to function 'is'.

Error in optimizer (line 105)
        if is(u{i},'complex')

Error in STLC_get_controller (line 375)
controller = optimizer([ Fs,Fdyn,Fstl,Fr_stl,
Fu],[],options,param_controller, output_controller);

Any help is greatly appreciated!

[johanlofberg]

Your output_controller argument is not an sdpvar

>> is(sdpvar,'complex')

ans =

  logical

   0

>> is([],'complex')
Check for missing argument or
incorrect argument data type in
call to function 'is'.
 
>> is(0,'complex')
Check for missing argument or
incorrect argument data type in
call to function 'is'.

[nbahari]

Thank you for your reply!