myffttrunc(s,n)

function S = myffttrunc(s,n)
%MYFFTTRUNC(s,n) returns the low-pass filtered content of the signal s
%   s      = s(x) where
%   x(:,j) = x(:,1)+(j-1)*(x(:,N)-x(:,1)+x(:,2)-x(:,1))/N, 
%   i = 1...N, N = 2^n
%
%   S is the low-passtruncated signal S = W*s, where W is the Fourier 
%   transfer function
%
%   See also myffttrunc2

%   Author(s): A. Almqvist
%   Copyright 2009- Andreas Almqvist
%   $Revision: 1$  $Date: 2009/11$
%   Homemade function

[M,N]   = size(s);

% Creating the transfer function W
wx  = (1:M/2-1);
                                    %            N/2+1
W1  = 1.*(wx<=n);                   %      W1      |    W2
W2  = fliplr(W1);                   %   ___________|______________wx 
                                    %
W   = [1,W1,1,W2].'*ones(1,N);      

% Truncating the signal in the frequency space and return it to the time
% domain
S   = real(ifft(W.*fft(s)));