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ltifr.m
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1999-03-05
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# Copyright (C) 1996 A. Scottedward Hodel
#
# 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, 675 Mass Ave, Cambridge, MA 02139, USA.
function out = ltifr(a,b,w)
#ltifr: Linear time invarient frequency response of SISO systems
# out = ltifr(A,B,w)
# user enters the A and B matrices
#
# out = ltifr(sys,w)
# user enters the system, SYS
#
# this function takes the system matrices, A and B and
# returns: -1
# G(s) = (jw I-A) B
#
# for complex frequencies s = jw.
# R. B. Tenison, D. Clem, A. S. Hodel, July 1995
# updated by John Ingram August 1996 for system format
if ((nargin < 2) || (nargin > 3))
error("incorrect number of input arguments");
endif
if (nargin == 2)
sys = a;
w = b;
if(!is_struct(sys))
error("two arguments: 1st must be a system data structure");
endif
if (!is_vector(w))
error("w must be a vector");
endif
[nn,nz,mm,pp] = sysdimensions(sys);
if(mm != 1) error("sys has %d > 1 inputs",mm); endif
[a,b] = sys2ss(sys);
else
if (columns(a) != rows(b)),
error("ltifr: A(%dx%d), B(%dx%d) not compatibly dimensioned", ...
rows(a), columns(a), rows(b), columns(b));
endif
if(columns(b) != 1)
error("ltifr: b(%dx%d) must be a single column vector", ...
rows(b),columns(b));
endif
if (!is_square(a))
error("ltifr: A(%dx$d) must be square.",rows(a),columns(a))
endif
endif
if (!is_vector(w))
error("w must be a vector");
endif
ey = eye(size(a));
lw = length(w);
out = ones(columns(a),lw);
for ii=1:lw,
out(:,ii) = (w(ii)*ey-a)\b;
endfor
endfunction