unitfeedback(sys1)

Creates the System Sys2(s)  from the system Sys1(s)
when we have a negative feedback.
____________
+   e    |            |
u --->0----->|   Sys1(s)  |------------> y
^-     |____________|      |
|                          |
|                          |
|                          |
--------------<-------------

and Returns :
Y(s)             Sys1(s)
Sys2(s)=  ------  =  -------------------
U(s)         1   +    Sys1(s)


the feedback is negative.
____________
|            |
u ---------->|   Sys2(s)  |------------> y
|____________|

This only works for SISO systems.