function [indmin, indmax, indzer] = extr(x,t);% [indmin, indmax, indzer] = EXTR(x,t) finds extrema and zero-crossings%% inputs : - x : analyzed signal%          - t (optional) : sampling times, default 1:length(x)%% outputs : - indmin = indices of minima%           - indmax = indices of maxima%           - indzer = indices of zero-crossings%%  originally done by:%   Rilling, G., Flandrin, P., and Goncalves, P. (2002)%       http://perso.ens-lyon.fr/patrick.flandrin/emd.html%  commented by Bradley Matthew Battista%   University of South Carolina%   Department of Geological Sciences%   701 Sumter Street, EWS 617%   Columbia, SC. 29208%% COPYRIGHT: see the associated COPYRIGHT.txt file, and also% http://software.seg.org/disclaimer2.txt% This source code may be found online at:% http://software.seg.org/2007/0003%if(nargin==1)  t=1:length(x);endm = length(x);x1=x(1:m-1);x2=x(2:m);indzer = find(x1.*x2<0); % find negative valuesif any(x == 0) % find existing zeros if any  iz = find( x==0 );  indz = [];  if any(diff(iz)==1) % find nonconsecutive zeros    zer = x == 0;    dz = diff([0 zer 0]);    debz = find(dz == 1); % find peak-side of a zero    finz = find(dz == -1)-1; % find trough-side of a zero    indz = round((debz+finz)/2); % avg peaks and troughs to get zero crossings  else    indz = iz;  end  indzer = sort([indzer indz]); % organize zero crossingsend  % take 2nd order derivative of x to find extremad = diff(x);n = length(d);d1 = d(1:n-1);d2 = d(2:n);indmin = find(d1.*d2<0 & d1<0)+1;indmax = find(d1.*d2<0 & d1>0)+1;% repeat for extrema not associated with a zero crossingif any(d==0)    imax = [];  imin = [];    bad = (d==0);  dd = diff([0 bad 0]);  debs = find(dd == 1);  fins = find(dd == -1);  if debs(1) == 1    if length(debs) > 1      debs = debs(2:end);      fins = fins(2:end);    else      debs = [];      fins = [];    end  end  if length(debs) > 0    if fins(end) == m      if length(debs) > 1        debs = debs(1:(end-1));        fins = fins(1:(end-1));      else        debs = [];        fins = [];      end          end  end  lc = length(debs);  if lc > 0    for k = 1:lc      if d(debs(k)-1) > 0        if d(fins(k)) < 0          imax = [imax round((fins(k)+debs(k))/2)];        end      else        if d(fins(k)) > 0          imin = [imin round((fins(k)+debs(k))/2)];        end      end    end  end    if length(imax) > 0    indmax = sort([indmax imax]);  end  if length(imin) > 0    indmin = sort([indmin imin]);  end  end