Iterative calculation of control signal by UDF and undefined variable error

There are two main problems about my simulation.

The first one is, eventhough I assign values to variables in my user defined function, I get the error below:

"Undefined function or variable 'var_name'. The first assignment to a local variable determines its class."

I solved it by equating the variables which are to be updated to zero and since my updated value is what I need, I have no problems about it. However, it doesn't seem to me that, this is an effective solution for this problem. What would you recommend?

Secondly,I don't think I successfully feed the last value of my variables to generate next values of them. Please, see the block, which is named "pid". Could you please check if the structure I use is right or wrong. If it is wrong, is there another way of performing this task?

Feel free to use the following info to initialize the simulation.

err = [0 0 0]
  w1 = rand(1)*ones(1,3)
  w2 =  rand(1)*ones(1,3)
  w3 =rand(1)*ones(1,3)
  I = [0 0 0]
  ctrl = 0

Thanks in advancce, Best regards.