www.pudn.com > hilbert.zip > extr.m, change:2008-02-23,size:1777b

```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

if(nargin==1)
t=1:length(x);
end

m = length(x);
x1=x(1:m-1);
x2=x(2:m);
indzer = find(x1.*x2<0);

if any(x == 0)
iz = find( x==0 );
indz = [];
if any(diff(iz)==1)
zer = x == 0;
dz = diff([0 zer 0]);
debz = find(dz == 1);
finz = find(dz == -1)-1;
indz = round((debz+finz)/2);
else
indz = iz;
end
indzer = sort([indzer indz]);
end

d = 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;

if any(d==0)

imax = [];
imin = [];

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
```