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+## Copyright (C) 1996, 1998 Auburn University.  All rights reserved.
+##
+## This file is part of Octave.
+##
+## Octave 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.
+##
+## Octave 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.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, write to the Free
+## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 USA.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{sys} =} sysscale (@var{sys}, @var{outscale}, @var{inscale}@{, @var{outname}, @var{inname}@})
+## scale inputs/outputs of a system.
+##
+## @strong{Inputs}
+## sys: structured system
+## outscale, inscale: constant matrices of appropriate dimension
+##
+## @strong{Outputs}
+## @var{sys}: resulting open loop system:
+## @example
+##       -----------    -------    -----------
+## u --->| inscale |--->| sys |--->| outscale |---> y
+##       -----------    -------    -----------
+## @end example
+## If the input names and output names (each a list of strings)
+## are not given and the scaling matrices
+## are not square, then default names will be given to the inputs and/or
+## outputs.
+##
+## A warning message is printed if outscale attempts to add continuous
+## system outputs to discrete system outputs; otherwise @var{yd} is
+## set appropriately in the returned value of @var{sys}.
+## @end deftypefn
+
+## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
+## Created: August 1995
+## modified by John Ingram 7-15-96
+
+function sys = sysscale (sys, outscale, inscale, outname, inname)
+
+  if( (nargin < 3) || (nargin > 5)  )
+    usage("retsys = sysscale(Asys,output_list,input_list{,inname,outname})");
+  elseif (!is_struct(sys))
+    error("sys must be a structured system");
+  endif
+
+  [nn,nz,mm,pp] = sysdimensions(sys);
+
+  ## check for omitted scales
+  if(isempty(outscale))    outscale = eye(pp);     endif
+  if(isempty(inscale))     inscale = eye(mm);      endif
+
+  ## check dimensions of scaling matrices
+  if(mm!=rows(inscale))
+    error("inscale(%dx%d) should have %d rows(# system inputs)", ...
+      rows(inscale),columns(inscale),mm);
+  elseif( pp != columns(outscale) )
+    error("outscale(%dx%d) should have %d columns(# system outputs)", ...
+      rows(outscale), columns(outscale),pp);
+  endif
+
+  sysyd = sysgetsignals(sys,"yd");
+  outc = find(sysyd==0);
+  outd = find(sysyd==1);
+
+  if(length(outc) & length(outd))
+    for ii = 1:rows(outscale)
+      nci = norm(outscale(ii,outc));
+      ndi = norm(outscale(ii,outd));
+
+      if( nci & ndi)
+        warning("sysscale: outscale(%d,:) sums continuous and discrete outputs; setting output to cont",ii)
+        sysyd(ii) = 0;
+      else
+        sysyd(ii) = (ndi != 0);
+      endif
+    endfor
+  else
+    sysyd = ones(1,rows(outscale))*( length(outd) > 0);
+  endif
+
+  ## check for SISO system type
+  if strcmp(sysgettype(sys),"tf")
+    [num,den,tsam,innam,outnam] = sys2tf(sys);
+    num = num*inscale*outscale;
+    sys = tf2sys(num,den,tsam,innam,outnam,find(sysyd));
+    return
+  elseif strcmp(sysgettype(sys),"zp")
+    [zer,pol,kk,tsam,innam,outnam] = sys2zp(sys);
+    kk = kk*inscale*outscale;
+    sys = zp2sys(zer,pol,k,tsam,innam,outnam,find(sysyd));
+    return
+  endif
+
+  ## it's a state space system...
+
+  [sysa,sysb,sysc,sysd,systsam, ...
+    sysn,sysnz,sysstname,sysinname,sysoutname,oldyd] = sys2ss(sys);
+
+  sysb = sysb*inscale;
+  sysc = outscale*sysc;
+  sysd = outscale*sysd*inscale;
+
+  if( !is_square(outscale) )
+    ## strip extra output names (if any)
+    sysoutname = sysoutname(1:min(rows(outscale),columns(outscale)));
+    if( nargin < 4)
+      warning("sysscale: outscale not square, outname not specified");
+      warning("sysscale:  using default output names");
+      outname = sysdefioname(rows(sysc),"y");
+    endif
+  else
+    outname = sysoutname;
+  endif
+  if( !is_square(inscale) )
+    ## strip extra output names (if any)
+    sysinname = sysinname(1:min(rows(inscale),columns(inscale)));
+    if(nargin < 5)
+      warning("sysscale: inscale not square, inname not specified");
+      warning("sysscale:  using default input names");
+      inname = sysdefioname(columns(sysb),"u");
+    endif
+  else
+    inname = sysgetsignals(sys,"in");
+  endif
+
+  sys = ss2sys(sysa,sysb,sysc,sysd,systsam,nn,nz,sysstname, ...
+        inname,outname,find(sysyd==1));
+
+endfunction