
%-*- texinfo -*-
%@deftypefn {Function} test_framemulappr
%@verbatim
% This test example is taken from demo_gabmulappr
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/deprecated/test_framemulappr.html}
%@end deftypefn

% Copyright (C) 2005-2023 Peter L. Soendergaard <peter@sonderport.dk> and others.
% This file is part of LTFAT version 2.6.0
%
% 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/>.

% Setup parameters for the Gabor system and length of the signal
L=576; % Length of the signal
a=32;   % Time shift 
M=72;  % Number of modulations
N=L/a;
fs=44100; % assumed sampling rate
SNRtv=63; % signal to noise ratio of change rate of time-variant system

% construction of slowly time variant system
% take an initial vector and multiply by random vector close to one
A = [];
c1=(1:L/2); c2=(L/2:-1:1); c=[c1 c2].^(-1); % weight of decay x^(-1)
A(1,:)=(tester_rand(1,L)-0.5).*c;  % convolution kernel
Nlvl = exp(-SNRtv/10);
Slvl = 1-Nlvl;
for ii=2:L;
     A(ii,:)=(Slvl*circshift(A(ii-1,:),[0 1]))+(Nlvl*(tester_rand(1,L)-0.5)); 
end;
A = A/norm(A)*0.99; % normalize matrix

% perform best approximation by gabor multiplier
g=gabtight(a,M,L);
sym1=gabmulappr(A,g,a,M);


% Now do the same using the general frame algorithm.

F=frame('dgt',g,a,M);

sym2=framemulappr(F,F,A);


norm(sym1-reshape(sym2,M,N))

% Test for exactness

testsym=tester_crand(M,N);
FT=frsynmatrix(F,L);

T=FT*diag(testsym(:))*FT';


sym1b=gabmulappr(T,g,a,M);
sym2b=framemulappr(F,F,T);

norm(testsym-sym1b)
norm(testsym-reshape(sym2b,M,N))

