function y = filtfilt(b,a,x)% FILTFILT Zero-phase forward and reverse digital filtering.%    Y = FILTFILT(B, A, X) filters the data in vector X with the%    filter described by vectors A and B to create the filtered data%    Y.%    %    After filtering in the forward direction, the filtered sequence%    is then reversed and run back through the filter; Y is the time%    reverse of the output of the second filtering operation. The%    result has precisely zero phase distortion and magnitude modified%    by the square of the filter's magnitude response. Care is taken%    to minimize startup and ending transients by matching initial%    conditions.% $Id: filtfilt.m 3 2004-02-04 12:57:04Z mairas $y_ = filtfilt(b,a,x.s);t = x.time;y = signal(y_,t);% set region of validityy.valid = x.valid;l = limpz(b,a,0.999,1024);y.valid(1) = x.valid(1)+l;if length(y.valid)==1  y.valid(2) = len(y)-l;else  y.valid(2) = x.valid(2)-l;end