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diff --git a/octave_packages/signal-1.1.3/pei_tseng_notch.m b/octave_packages/signal-1.1.3/pei_tseng_notch.m
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+## Copyright (C) 2011 Alexander Klein <alexander.klein@math.uni-giessen.de>
+##
+## 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/>.
+
+## -*- texinfo -*-
+## @deftypefn{Function File} { [ @var{b}, @var{a} ] } = pei_tseng_notch ( @var{frequencies}, @var{bandwidths}
+## Return coefficients for an IIR notch-filter with one or more filter frequencies and according (very narrow) bandwidths
+## to be used with @code{filter} or @code{filtfilt}.
+## The filter construction is based on an allpass which performs a reversal of phase at the filter frequencies.
+## Thus, the mean of the phase-distorted and the original signal has the respective frequencies removed.
+## See the demo for an illustration.
+##
+## Original source:
+## Pei, Soo-Chang, and Chien-Cheng Tseng
+## "IIR Multiple Notch Filter Design Based on Allpass Filter"
+## 1996 IEEE Tencon
+## doi: 10.1109/TENCON.1996.608814)
+## @end deftypefn
+
+## TODO: Implement Laplace-space frequencies and bandwidths, and perhaps better range checking for bandwidths?
+
+function [ b, a ] = pei_tseng_notch ( frequencies, bandwidths )
+
+  err = nargchk ( 2, 2, nargin, "string" );
+
+  if ( err )
+    error ( err );
+  elseif ( !isvector ( frequencies ) || !isvector ( bandwidths ) )
+    error ( "All arguments must be vectors!" )
+  elseif ( length ( frequencies ) != length ( bandwidths ) )
+    error ( "All arguments must be of equal length!" )
+  elseif ( !all ( frequencies > 0 && frequencies < 1 ) )
+    error ( "All frequencies must be in (0, 1)!" )
+  elseif ( !all ( bandwidths > 0 && bandwidths < 1 ) )
+    error ( "All bandwidths must be in (0, 1)!" )
+  endif
+
+  ##Ensure row vectors
+  frequencies = frequencies (:)';
+  bandwidths  = bandwidths (:)';
+
+
+  ##Normalise appropriately
+  frequencies *= pi;
+  bandwidths  *= pi;
+  M2           = 2 * length ( frequencies );
+
+
+  ##Splice centre and offset frequencies ( Equation 11 )
+  omega = vec ( [ frequencies - bandwidths / 2; frequencies ] );
+
+  ##Splice centre and offset phases ( Equations 12 )
+  factors = ( 1 : 2 : M2 );
+  phi     = vec ( [ -pi * factors + pi / 2; -pi * factors ] );
+
+  ##Create linear equation
+  t_beta = tan ( ( phi + M2 * omega ) / 2 );
+
+  Q = zeros ( M2 );
+
+  for k = 1 : M2
+    Q ( : ,k ) = sin ( k .* omega ) - t_beta .* cos ( k .* omega );
+  endfor
+
+  ##Compute coefficients of system function ( Equations 19, 20 ) ...
+  h_a   = ( Q \ t_beta )' ;
+  denom = [ 1, h_a ];
+  num   = [ fliplr( h_a ), 1 ];
+
+  ##... and transform them to coefficients for difference equations
+  a = denom;
+  b = ( num + denom ) / 2;
+
+endfunction
+
+%!test
+%! ##2Hz bandwidth
+%! sf = 800; sf2 = sf/2;
+%! data=[sinetone(49,sf,10,1),sinetone(50,sf,10,1),sinetone(51,sf,10,1)];
+%! [b, a] = pei_tseng_notch ( 50 / sf2, 2 / sf2 );
+%! filtered = filter ( b, a, data );
+%! damp_db = 20 * log10 ( max ( filtered ( end - 1000 : end, : ) ) );
+%! assert ( damp_db, [ -3 -251.9 -3 ], 0.1 )
+
+%!test
+%! ##1Hz bandwidth
+%! sf = 800; sf2 = sf/2;
+%! data=[sinetone(49.5,sf,10,1),sinetone(50,sf,10,1),sinetone(50.5,sf,10,1)];
+%! [b, a] = pei_tseng_notch ( 50 / sf2, 1 / sf2 );
+%! filtered = filter ( b, a, data );
+%! damp_db = 20 * log10 ( max ( filtered ( end - 1000 : end, : ) ) );
+%! assert ( damp_db, [ -3 -240.4 -3 ], 0.1 )
+
+%!demo
+%! sf = 800; sf2 = sf/2;
+%! data=[[1;zeros(sf-1,1)],sinetone(49,sf,1,1),sinetone(50,sf,1,1),sinetone(51,sf,1,1)];
+%! [b,a]=pei_tseng_notch ( 50 / sf2, 2/sf2 );
+%! filtered = filter(b,a,data);
+%!
+%! clf
+%! subplot ( columns ( filtered ), 1, 1) 
+%! plot(filtered(:,1),";Impulse response;")
+%! subplot ( columns ( filtered ), 1, 2 ) 
+%! plot(filtered(:,2),";49Hz response;")
+%! subplot ( columns ( filtered ), 1, 3 ) 
+%! plot(filtered(:,3),";50Hz response;")
+%! subplot ( columns ( filtered ), 1, 4 ) 
+%! plot(filtered(:,4),";51Hz response;")