function [maxtab, mintab]=peakdet(v, delta, x)
%PEAKDET Detect peaks in a vector
%        [MAXTAB, MINTAB] = PEAKDET(V, DELTA) finds the local
%        maxima and minima ("peaks") in the vector V.
%        MAXTAB and MINTAB consists of two columns. Column 1
%        contains indices in V, and column 2 the found values.
%      
%        With [MAXTAB, MINTAB] = PEAKDET(V, DELTA, X) the indices
%        in MAXTAB and MINTAB are replaced with the corresponding
%        X-values.
%
%        A point is considered a maximum peak if it has the maximal
%        value, and was preceded (to the left) by a value lower by
%        DELTA.

% Eli Billauer, 3.4.05 (Explicitly not copyrighted).
% This function is released to the public domain; Any use is allowed.

maxtab = [];
mintab = [];

v = v(:); % Just in case this wasn't a proper vector

if nargin < 3
  x = (1:length(v))';
else 
  x = x(:);
  if length(v)~= length(x)
    error('Input vectors v and x must have same length');
  end
end
  
if (length(delta(:)))>1
  error('Input argument DELTA must be a scalar');
end

if delta <= 0
  error('Input argument DELTA must be positive');
end

mn = Inf; mx = -Inf;
mnpos = NaN; mxpos = NaN;

lookformax = 1;

for i=1:length(v)
  this = v(i);
  if this > mx, mx = this; mxpos = x(i); end
  if this < mn, mn = this; mnpos = x(i); end
  
  if lookformax
    if this < mx-delta
      maxtab = [maxtab ; mxpos mx];
      mn = this; mnpos = x(i);
      lookformax = 0;
    end  
  else
    if this > mn+delta
      mintab = [mintab ; mnpos mn];
      mx = this; mxpos = x(i);
      lookformax = 1;
    end
  end
end

function [maxtab, mintab]=peakdet(v, delta, x)
%v,x轴顺序取值（1、2、...10001）时，对应的y轴的值
%delta 差值 △X的意思
%x,x轴顺序取值（1、2、...10001）
%maxtab 二维数组,类似于坐标图上的点坐标集合，每个点point（x,y）表示，它有n个point组成
%maxtab 第一列：顺序存放点的x坐标值,第二列：顺序存放与x轴点对应的的y坐标值，
%maxtab 每一行存放一个坐标点point（x,y）
%PEAKDET Detect peaks in a vector
%        [MAXTAB, MINTAB] = PEAKDET(V, DELTA) finds the local
%        maxima and minima ("peaks") in the vector V.
%        MAXTAB and MINTAB consists of two columns. Column 1
%        contains indices in V, and column 2 the found values.
%      
%        With [MAXTAB, MINTAB] = PEAKDET(V, DELTA, X) the indices
%        in MAXTAB and MINTAB are replaced with the corresponding
%        X-values.
%
%        A point is considered a maximum peak if it has the maximal
%        value, and was preceded (to the left) by a value lower by
%        DELTA.

% Eli Billauer, 3.4.05 (Explicitly not copyrighted).
% This function is released to the public domain; Any use is allowed.

maxtab = [];%存放峰点坐标
mintab = [];%存放谷点坐标

v = v(:); % Just in case this wasn't a proper vector

if nargin < 3 %nargin:输入变量的个数
  x = (1:length(v))'; %1到10001
else 
  x = x(:);
  if length(v)~= length(x) %~= 不等于 
    error('Input vectors v and x must have same length');
  end
end
  
if (length(delta(:)))>1 %输入delta只能是一个值  并且大于等于0
  error('Input argument DELTA must be a scalar'); %scalar 标量
end

if delta <= 0
  error('Input argument DELTA must be positive');
end

mn = Inf; mx = -Inf;  %inf 当算出的结果大于某个数（这个数很大，
                      %比如10的很多次方），则MATLAB认为就是无穷大了，并返回 inf
mnpos = NaN; mxpos = NaN; % NaN:Not  a  Number 类似初始化赋值

lookformax = 1; %取峰和谷的标记  1:取峰，0取谷

for i=1:length(v) %length(v) v中值的个数 10001个
  this = v(i);%v(i)代表第i个点y轴值
  if this > mx, mx = this; mxpos = x(i); end %x(i)代表第i个点x轴值
  if this < mn, mn = this; mnpos = x(i); end
  
  if lookformax
    if this < mx-delta %y轴值的比较  满足该条件的点在峰的右边
      maxtab = [maxtab ; mxpos mx]; %给maxtab（二维向量）赋值，x轴值mxpos，y轴值mx
      mn = this; mnpos = x(i);
      lookformax = 0; %已取到峰，下一次取谷
    end  
  else
    if this > mn+delta %y轴值的比较  满足该条件的点在谷的右边
      mintab = [mintab ; mnpos mn];
      mx = this; mxpos = x(i);
      lookformax = 1; %已取到谷，下一次取峰
    end
  end
end