/trunk/octave-forge/main/signal/inst/besself.m
Objective C | 117 lines | 103 code | 14 blank | 0 comment | 25 complexity | 30de67237cc15cfbff26337c6b12c5f2 MD5 | raw file
Possible License(s): GPL-2.0, BSD-3-Clause, LGPL-2.1, GPL-3.0, LGPL-3.0
- ## Copyright (C) 1999 Paul Kienzle <pkienzle@users.sf.net>
- ## Copyright (C) 2003 Doug Stewart <dastew@sympatico.ca>
- ## Copyright (C) 2009 Thomas Sailer <t.sailer@alumni.ethz.ch>
- ##
- ## 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; if not, see <http://www.gnu.org/licenses/>.
- ## Generate a bessel filter.
- ## Default is a Laplace space (s) filter.
- ##
- ## [b,a] = besself(n, Wc)
- ## low pass filter with cutoff pi*Wc radians
- ##
- ## [b,a] = besself(n, Wc, 'high')
- ## high pass filter with cutoff pi*Wc radians
- ##
- ## [b,a] = besself(n, [Wl, Wh])
- ## band pass filter with edges pi*Wl and pi*Wh radians
- ##
- ## [b,a] = besself(n, [Wl, Wh], 'stop')
- ## band reject filter with edges pi*Wl and pi*Wh radians
- ##
- ## [z,p,g] = besself(...)
- ## return filter as zero-pole-gain rather than coefficients of the
- ## numerator and denominator polynomials.
- ##
- ## [...] = besself(...,'z')
- ## return a discrete space (Z) filter, W must be less than 1.
- ##
- ## [a,b,c,d] = besself(...)
- ## return state-space matrices
- ##
- ## References:
- ##
- ## Proakis & Manolakis (1992). Digital Signal Processing. New York:
- ## Macmillan Publishing Company.
- function [a, b, c, d] = besself (n, W, varargin)
-
- if (nargin>4 || nargin<2) || (nargout>4 || nargout<2)
- print_usage;
- end
- ## interpret the input parameters
- if (!(length(n)==1 && n == round(n) && n > 0))
- error ("besself: filter order n must be a positive integer");
- end
- stop = 0;
- digital = 0;
- for i=1:length(varargin)
- switch varargin{i}
- case 's', digital = 0;
- case 'z', digital = 1;
- case { 'high', 'stop' }, stop = 1;
- case { 'low', 'pass' }, stop = 0;
- otherwise, error ("besself: expected [high|stop] or [s|z]");
- endswitch
- endfor
- [r, c]=size(W);
- if (!(length(W)<=2 && (r==1 || c==1)))
- error ("besself: frequency must be given as w0 or [w0, w1]");
- elseif (!(length(W)==1 || length(W) == 2))
- error ("besself: only one filter band allowed");
- elseif (length(W)==2 && !(W(1) < W(2)))
- error ("besself: first band edge must be smaller than second");
- endif
- if ( digital && !all(W >= 0 & W <= 1))
- error ("besself: critical frequencies must be in (0 1)");
- elseif ( !digital && !all(W >= 0 ))
- error ("besself: critical frequencies must be in (0 inf)");
- endif
- ## Prewarp to the band edges to s plane
- if digital
- T = 2; # sampling frequency of 2 Hz
- W = 2/T*tan(pi*W/T);
- endif
- ## Generate splane poles for the prototype bessel filter
- [zero, pole, gain] = besselap(n);
- ## splane frequency transform
- [zero, pole, gain] = sftrans(zero, pole, gain, W, stop);
- ## Use bilinear transform to convert poles to the z plane
- if digital
- [zero, pole, gain] = bilinear(zero, pole, gain, T);
- endif
- ## convert to the correct output form
- if nargout==2,
- a = real(gain*poly(zero));
- b = real(poly(pole));
- elseif nargout==3,
- a = zero;
- b = pole;
- c = gain;
- else
- ## output ss results
- [a, b, c, d] = zp2ss (zero, pole, gain);
- endif
- endfunction