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function [gh,gd,g]=comp_phasegradfilters(g,a,L)
%-*- texinfo -*-
%@deftypefn {Function} comp_phasegradfilters
%@verbatim
% Number of filters
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/comp/comp_phasegradfilters.html}
%@end deftypefn
% Copyright (C) 2005-2016 Peter L. Soendergaard <peter@sonderport.dk>.
% This file is part of LTFAT version 2.3.1
%
% 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/>.
M = numel(g);
% Precompute filters for length L if not done already
g = comp_filterbank_pre(g,a,L,100);
% Divide filters to time domain and frequency domain groups
mFreqBl = 1:M;
mTime = mFreqBl(cellfun(@(gEl) isfield(gEl,'h'),g(:))>0);
mFreqBl(mTime) = [];
mFreqL = mFreqBl(cellfun(@(gEl) isfield(gEl,'H') && numel(gEl.H) == L,g)>0);
mFreqBl(mFreqL) = [];
% For FIR/full-length frequency response filters, compute center frequency
if numel(mFreqBl) < M
cfreq = zeros(M,1);
tempind = [mTime,mFreqL];
cfreq(tempind) = round(L/2*cent_freqs(g(tempind),L));
end;
% Determine impulse response or transfer function length
Lg = L*ones(M,1);
Lg(mTime) = cellfun(@(gEl) length(gEl.h),g(mTime));
Lg(mFreqBl) = cellfun(@(gEl) length(gEl.H),g(mFreqBl));
gh = g;
gd = g;
fftind = fftindex(L,0); % Set Nyquist frequency to 0!
%% ------ algorithm starts --------------------
% Construct time/frequency weighted versions of filters
% defined on the time side
for mId = mTime
% Compute time weighted version.
tempind = (g{mId}.offset:Lg(mId)+g{mId}.offset-1).';
gh{mId}.h = tempind.*g{mId}.h;
% Compute frequency weighted version.
gH = comp_transferfunction(g{mId},L);
gd{mId}.H = circshift(fftind,cfreq(mId)).*gH;
gd{mId}=rmfield(gd{mId},'h');
gd{mId}=rmfield(gd{mId},'offset');
gd{mId}.foff = 0;
end;
% Construct time/frequency weighted versions of bandlimited filters
% defined on the frequency side
for mId = mFreqBl
% Compute frequency weighted version.
tempind = [L-floor(Lg(mId)/2)+1:L, ...
1:ceil(Lg(mId)/2)];
gd{mId}.H = fftind(tempind).*g{mId}.H;
% Compute time weighted version.
% The code below is a quick and dirty version of
% longg = fftshift(g{mId}.H);
% gd2{mId}.H = fftshift(pderiv(longg,[],Inf)/(2*pi));
n=fftindex(Lg(mId),0);
gh{mId}.H = L/Lg(mId)*real(fftshift( ...
ifft(1i.*n.*fft(fftshift(g{mId}.H)))));
end;
% Construct time/frequency weighted versions of full-length filters
% defined on the frequency side
for mId = mFreqL
% Compute frequency weighted version.
gd{mId}.H = circshift(fftind,cfreq(mId)).*g{mId}.H;
% Compute time weighted version.
gh{mId}.H = real(ifft(1i.*fftind.*fft(g{mId}.H)));
end;
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