abcd(1)

NAME
feedback - feedback operation

CALLING SEQUENCE
Sl=Sl1/.Sl2

PARAMETERS

Sl1,Sl2
    : linear systems (syslin list) in state-space or transfer form, or ordinary gain matrices.

Sl  : linear system (syslin list) in state-space or transfer form

DESCRIPTION
The feedback operation is denoted by /. (slashdot). This command returns Sl=Sl1*(I+Sl2*Sl1)^-1, i.e the (negative) feedback of Sl1 and Sl2.

The result is the same as Sl=LFT([0,I;I,-Sl2],Sl1).

Caution: do not use with decimal point (e.g. 1/.1 is ambiguous!)

EXAMPLE
S1=ssrand(2,2,3);S2=ssrand(2,2,2);
W=S1/.S2;
ss2tf(S1/.S2)
//Same operation by LFT:
ss2tf(lft([zeros(2,2),eye(2,2);eye(2,2),-S2],S1))
//Other approach: with constant feedback
BigS=sysdiag(S1,S2); F=[zeros(2,2),eye(2,2);-eye(2,2),zeros(2,2)];
Bigclosed=BigS/.F;
W1=Bigclosed(1:2,1:2);   //W1=W (in state-space).
ss2tf(W1)

SEE ALSO
lft, sysdiag, augment