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function out=spreadinv(p1,p2);
%-*- texinfo -*-
%@deftypefn {Function} spreadinv
%@verbatim
%SPREADINV Apply inverse spreading operator
% Usage: h=spreadinv(f,c);
%
% SPREADINV(c) computes the symbol of the inverse of the spreading
% operator with symbol c.
%
% SPREADINV(f,c) applies the inverse of the spreading operator with
% symbol c to the input signal f.
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/operators/spreadinv.html}
%@seealso{spreadfun, tconv, spreadfun, spreadadj}
%@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/>.
complainif_argnonotinrange(nargin,1,2,mfilename);
% FIXME This function should handle sparse symbols, and use a iterative
% method instead of creating the full symbol.
% FIXME This function should handle f though comp_reshape_pre and post.
if nargin==1
coef=p1;
else
f=p1;
coef=p2;
end;
if ndims(coef)>2 || size(coef,1)~=size(coef,2)
error('Input symbol T must be a square matrix.');
end;
L=size(coef,1);
% Create a matrix representation of the operator.
coef=ifft(full(coef))*L;
T=comp_col2diag(coef);
if nargin==1
% Calculate the inverse symbol.
out=spreadfun(inv(T));
else
out=T\f;
end;
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