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ltifr.m
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1999-12-24
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## Copyright (C) 1996 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{out} =} ltifr (@var{A}, @var{B}, @var{w})
## @deftypefnx {Function File } {@var{out} =} ltifr (@var{sys}, @var{w})
## Linear time invariant frequency response of single input systems
## @strong{Inputs}
## @table @var
## @item A, B
## coefficient matrices of @math{dx/dt = A x + B u}
## @item sys
## system data structure
## @item w
## vector of frequencies
## @end table
## @strong{Outputs}
## @var{out}
## @example
## -1
## G(s) = (jw I-A) B
## @end example
## for complex frequencies @math{s = jw}.
## @end deftypefn
function out = ltifr (a, b, w)
## 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_vec(w))
error("w must be a vector");
endif
[nn,nz,mm,pp] = sysdimen(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_sqr(a))
error("ltifr: A(%dx$d) must be square.",rows(a),columns(a))
endif
endif
if (!is_vec(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