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## Copyright (C) 1996, 1998, 2004, 2005, 2006, 2007
## Auburn University. 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 3 of the License, or (at
## your option) any later version.
##
## This program 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 this program; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} tf (@var{num}, @var{den}, @var{tsam}, @var{inname}, @var{outname})
## build system data structure from transfer function format data
##
## @strong{Inputs}
## @table @var
## @item num
## @itemx den
## coefficients of numerator/denominator polynomials
## @item tsam
## sampling interval. default: 0 (continuous time)
## @item inname
## @itemx outname
## input/output signal names; may be a string or cell array with a single string
## entry.
## @end table
##
## @strong{Outputs}
## @var{sys} = system data structure
##
## @strong{Example}
## @example
## octave:1> sys=tf([2 1],[1 2 1],0.1);
## octave:2> sysout(sys)
## Input(s)
## 1: u_1
## Output(s):
## 1: y_1 (discrete)
## Sampling interval: 0.1
## transfer function form:
## 2*z^1 + 1
## -----------------
## 1*z^2 + 2*z^1 + 1
## @end example
## @end deftypefn
## Author: R. Bruce Tenison <btenison@eng.auburn.edu>
## Created: July 29, 1994
## Name changed to TF2SYS July 1995
## updated for new system data structure format July 1996
function outsys = tf (num, den, tsam, inname, outname)
## Test for the correct number of input arguments
if (nargin < 2 || nargin > 5)
print_usage ();
endif
## check input format
if (! ((isvector (num) || isscalar (num))
&& (isvector (den) || isscalar (den))))
error ("num (%dx%d) and den (%dx%d) must be vectors",
rows (num), columns (num), rows (den), columns (den));
endif
## strip leading zero coefficients
num = __tfl__ (num);
den = __tfl__ (den);
if (length (num) > length (den))
error ("# of poles (%d) < # of zeros (%d)", length(den)-1, length(num)-1);
endif
## check sampling interval (if any)
if (nargin <= 2)
tsam = 0; # default
elseif (isempty (tsam))
tsam = 0;
endif
if (! (isscalar (tsam) && imag (tsam) == 0) || tsam < 0)
error ("tsam must be a positive real scalar")
endif
outsys.num = num;
outsys.den = den;
## Set the system vector: active = 0(tf), updated = [1 0 0];
outsys.sys = [0, 1, 0, 0];
## Set defaults
outsys.tsam = tsam;
outsys.n = length (den) - 1;
outsys.nz = 0;
outsys.yd = 0; # assume discrete-time
## check discrete time
if (tsam > 0)
[outsys.n, outsys.nz] = swap (outsys.n, outsys.nz);
outsys.yd = 1;
endif
outsys.inname = __sysdefioname__ (1, "u");
outsys.outname = __sysdefioname__ (1, "y");
outsys.stname = __sysdefstname__ (outsys.n, outsys.nz);
## Set name of input
if (nargin > 3)
## make sure it's a cell array of a single string
if (! isempty (inname))
if (! iscell (inname))
inname = {inname};
endif
if (! is_signal_list (inname))
error ("inname must be a string or cell array of strings");
endif
if (length (inname) > 1)
warning ("tf: %d input names provided; first used", length (inname));
inname = inname(1);
endif
outsys = syssetsignals (outsys, "in", inname);
endif
endif
## Set name of output
if (nargin > 4)
if (! isempty (outname))
if (! iscell (outname))
outname = {outname};
endif
if (! is_signal_list (outname))
error ("outname must be a string or a cell array of strings");
endif
if (length (outname) > 1)
warning ("tf: %d output names provided; first used", length(outname));
outname = outname(1);
endif
outsys = syssetsignals (outsys, "out", outname);
endif
endif
endfunction
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