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tf.m
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tf.m
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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 ();
end
%% 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));
end
%% 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);
end
%% check sampling interval (if any)
if (nargin <= 2)
tsam = 0
elseif (isempty (tsam))
tsam = 0;
end
if (~ (isscalar (tsam) & imag (tsam) == 0) | tsam < 0)
error ('tsam must be a positive real scalar')
end
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
%% check discrete time
if (tsam > 0)
[outsys.n, outsys.nz] = swap (outsys.n, outsys.nz);
outsys.yd = 1;
end
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};
end
if (~ is_signal_list (inname))
error ('inname must be a string or cell array of strings');
end
if (length (inname) > 1)
warning ('tf: %d input names provided; first used', length (inname));
inname = inname(1);
end
outsys = syssetsignals (outsys, 'in', inname);
end
end
%% Set name of output
if (nargin > 4)
if (~ isempty (outname))
if (~ iscell (outname))
outname = {outname};
end
if (~ is_signal_list (outname))
error ('outname must be a string or a cell array of strings');
end
if (length (outname) > 1)
warning ('tf: %d output names provided; first used', length(outname));
outname = outname(1);
end
outsys = syssetsignals (outsys, 'out', outname);
end
end
end