Hi Tenzing,
From my understanding, you are trying to give positive feedback to your system and gain of feedback block is one. But your system has 2 inputs and 4 outputs. So, you need to mention from which output you would like to give feedback to which input of the system.
For example:
feedin=[1]; % feedback should be given to 1st input of the block
feedout=[1]; %feedback is taken from 1st output of the block
sys_cl=feedback(hzpk,1,feedin,feedout,1); % first one represents the gain of the feedback block and the other one represents the positive feedback
For knowing no.of inputs and outputs of the system
size(hzpk);
For more information refer the documentation below:
Hope this helps!
