extr函数
请问各位高手，在这个函数中，带红色的部分是什么意思呢？通过x1=x(1:m-1);
x2=x(2:m);
indzer = find(x1.*x2<0);
这几个语句，不是可以求出来极值点的位置吗？
function = extr(x,t);
% = 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();
debz = find(dz == 1);
finz = find(dz == -1)-1;
indz = round((debz+finz)/2);
else
indz = iz;
end
indzer = sort();
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 = [];
bad = (d==0);
dd = diff();
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 = ;
end
else
if d(fins(k)) > 0
imin = ;
end
end
end
end
if length(imax) > 0
indmax = sort();
end
if length(imin) > 0
indmin = sort();
end
end if any(diff(iz)==1) % find nonconsecutive zeros
zer = x == 0;
dz = diff();
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
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