From sources-request at octave dot org Sat Dec 31 08:35:58 2005
Subject: Addon to OCST - Matlab c2d "FOH" method
From: =?iso-8859-1?Q?Olof_T=E5ngrot?= <olof dot tangrot at telia dot com>
To: <sources at octave dot org>
Date: Sat, 31 Dec 2005 07:29:35 -0600

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Control theory command c2d in Octave and Matlab has similar features. Though
the triangle hold equvivalence (or first order hold) is not availible in the 
Octave version.

The appended code originates from the M-files found at 
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectType=file&objectId=2163 
(tri.m).
The code applies to the book Digital Control of Dynamic Systems by Franklin 
et. al, 2nd and 3rd edition.

I have modified it to work with OCST system structures and tested it with a 
SISO system.

It can be used as is or could be added to the existing c2d command.

Please consider including them into the distribution. As far as I can tell 
from the readme.m the authors place no restrictions on modification or 
redistribution.

Olof Tångrot 

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function dsys =3D trieq_oct(SYS,T)=0A=
##  dsys =3D trieq_oct(sys,T) computes the discrete time =0A=
##  triangle hold equivalent of purely contiouns system=0A=
##  SYS at sampling period T.=0A=
##=0A=
##  The triangle hold equvialent is described in =0A=
##  Digital Control of Dynamic Systems, Franklin et. al, 2nd edtion, =0A=
##  page 151-155.=0A=
=0A=
if(!(0 =3D=3D is_digital(SYS)))=0A=
  error("trieq: system is not purely contionous") % Mayby this =
restriction could be removed.=0A=
else=0A=
  [a,b,c,d,tsam,n,nz,stname,inname,outname,yd] =3D sys2ss(SYS);=0A=
  stnamed =3D strappend(stname,"_d");=0A=
  [n,n] =3D size(a);=0A=
  [ny,nx] =3D size(c);=0A=
  cc =3D zeros(ny,nx);=0A=
  [nx,nu] =3D size(b);=0A=
  bb =3D zeros(nx,nu);=0A=
  aa =3D [a b bb ; cc 0 1/T; cc 0 0]; % Create big matrix=0A=
  pp =3D expm(aa*T);=0A=
  f =3D pp(1:n,1:n);=0A=
  gamma1 =3D pp(1:n,n+1);=0A=
  gamma2 =3D pp(1:n,n+2);=0A=
  g =3D gamma1 + f*gamma2 - gamma2;=0A=
  h =3D c;=0A=
  j =3D d + c*gamma2;=0A=
  dsys =3D ss(f,g,h,j,T,0,rows(f),stnamed,inname,outname);=0A=
endif=0A=

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