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## Copyright (C) 2007 ZYED ben Mohamed EL HIDRI. 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.
##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.
## Author: Zyed El Hidri <zyedm79@yahoo.com>
function out = unitfeedback(sys)
if (nargin != 1)
error("only 1 arguements accepted");
endif
if(!is_siso(sys))
error("only single input single output systems supported");
endif
S=ss([],[],[],[1,-1],0,0,0,[],{"r(t)","y(t)",},"e(t)");
PS=sysmult(sys,S);
Pcl=sysconnect(PS,1,2);
out=sysprune(Pcl,1,1);
endfunction
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