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## Copyright (C) 2000 Ben Sapp. All rights reserved.
##
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by the
## Free Software Foundation; either version 2, or (at your option) any
## later version.
##
## This is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
## for more details.
## feedback(sys1,sys2)
##
## Filter the output of sys1 through sys2 and subtract it from the input.
##
## _____________
## + | |
## u --->0----->| sys1 |------->
## |- |____________| |
## | |
## | _____________ |
## | | | |
## -------| sys2 |----
## |____________|
##
## This only works for SISO systems.
## Author: Ben Sapp <bsapp@lanl.gov>
function out = feedback(sys1,sys2)
if (nargin != 2)
error("only 2 arguements accepted");
endif
if(!is_siso(sys1) || !is_siso(sys2))
error("only single input single output systems supported");
endif
T = sysgroup(sys1,sys2);
T = sysdup(T,2,[]);
T = sysscale(T,diag([1,1,-1]),[]);
T = sysconnect(T,3,1);
T = sysconnect(T,1,2);
out = sysprune(T,1,1);
endfunction
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