function imf = emd(x)
% Empiricial Mode Decomposition (Hilbert-Huang Transform)
% imf = emd(x)
% Func : findpeaks
x= transpose(x(:))%转置基颂为行矩阵
imf = []
while ~ismonotonic(x) %当x不是单调函数,分解终止条件
x1 = x
sd = Inf%均值
%直到x1满足IMF条件,得c1
while (sd >0.1) | ~isimf(x1) %当标准偏差系数sd大于0.1或x1不是固有模态函数时,分量终搏肆郑止条件
s1 = getspline(x1)%上包络线
s2 = -getspline(-x1)%下包络线
x2 = x1-(s1+s2)/2%此处的x2为文章中的h
sd = sum((x1-x2).^2)/sum(x1.^2)
x1 = x2
end
imf{end+1} = x1
x = x-x1
end
imf{end+1} = x
% FUNCTIONS
function u = ismonotonic(x)
%u=0表示x不是单调函数,u=1表示x为单调的
u1 = length(findpeaks(x))*length(findpeaks(-x))
if u1 >0, u = 0
else, u = 1end
function u = isimf(x)
%u=0表示x不是固有模式函数,u=1表示x是固有模式函数
N = length(x)
u1 = sum(x(1:N-1).*x(2:N) <0)
u2 = length(findpeaks(x))+length(findpeaks(-x))
if abs(u1-u2) >1, u = 0
else, u = 1end
function s = getspline(x)
%三次样条函数拟合成元数据包络线
N = length(x)
p = findpeaks(x)
s = spline([0 p N+1],[0 x(p) 0],1:N)
-------------------------------------------------------------------------------
--------------------------------------------------------------------------------
function n = findpeaks(x)
% Find peaks.找到极值 ,n为极值点所在位置
% n = findpeaks(x)
n= find(diff(diff(x) >0) <0)
u= find(x(n+1) >x(n))
n(u) = n(u)+1
------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
function plot_hht00(x,Ts)
% 双雹首边带调幅信号的EMD分解
% Plot the HHT.
% plot_hht(x,Ts)
%
% :: Syntax
%The array(列) x is the input signal and Ts is the sampling period(取样周期).
%Example on use: [x,Fs] = wavread('Hum.wav')
%plot_hht(x(1:6000),1/Fs)
% Func : emd
% Get HHT.
clear all
close all
Ts=0.0005
t=0:Ts:10 % 采样率2000HZ
% 调幅信号
%x=sin(2*pi*t).*sin(40*pi*t)
x=sin(2*pi*t)
s1 = getspline(x)%上包络线
s2 = -getspline(-x)%上包络线
x1 = (s1+s2)/2%此处的x2为文章中的h
figure
plot(t,x)xlabel('Time'), ylabel('Amplitude')title('双边带调幅信号')hold on
plot(t,s1,'-r')
plot(t,s2,'-r')
plot(t,x1,'g')
imf = emd(x)
for k = 1:length(imf)
b(k) = sum(imf{k}.*imf{k})
th = angle(hilbert(imf{k}))
d{k} = diff(th)/Ts/(2*pi)
end
[u,v] = sort(-b)
b = 1-b/max(b)
% Set time-frequency plots.
N = length(x)
c = linspace(0,(N-2)*Ts,N-1)
%
figure
for k = v(1:2)
plot(c,d{k},'k.','Color',b([k k k]),'MarkerSize',3)hold on
set(gca,'FontSize',8,'XLim',[0 c(end)],'YLim',[0 50])%设置x、y轴句柄
xlabel('Time'), ylabel('Frequency')title('原信号时频图')
end
% Set IMF plots.
M = length(imf)
N = length(x)
c = linspace(0,(N-1)*Ts,N)
for k1 = 0:4:M-1
figure
for k2 = 1:min(4,M-k1),
subplot(4,1,k2),
plot(c,imf{k1+k2})
set(gca,'FontSize',8,'XLim',[0 c(end)])
title('EMD分解结果')
end
xlabel('Time')
end
一般的的查询可在matlab里的帮助界面进行搜索,点击帮助。打开帮助页面,左侧检索栏进行检索需要查询的语句,然后即可查看右侧谨老孝查询结果。
或者在主界面,输入help 空格+你要查询的内容,进行查询。下次你可以尝试一下。
一般程序都会有不懂得语句,或没用过的,可以在刚刚说过的帮助页面进行查询,看如何使用,输入参量什么意义,程序输出结果是什么。
你这个描述祥稿太过于简略了,含氏我只能给出这样的答案了,一般可以都给一点程序,也许会有对答题人帮助。
不过你这个程序的确有点复杂,不根据前后逻辑,和主程序和目的是很难解答的。
你可以看看主程序,再查查帮助。
希望对你有所帮助。谢谢。
function imf = emd(x,n)%%最好把函数名改为emd1之类的,以免和Grilling的emd冲突%%n为你想得到的IMF的个数
c = x('% copy of the input signal (as a row vector)
N = length(x)-
% loop to decompose the input signal into n successive IMFs
imf = []% Matrix which will contain the successive IMF, and the residuefor t=1:n
% loop on successive IMFs
%-------------------------------------------------------------------------
% inner loop to find each imf
h = c% at the beginning of the sifting process, h is the signal
SD = 1% Standard deviation which will be used to stop the sifting process
while SD >0.3 % while the standard deviation is higher than 0.3 (typical value) %%筛选停止准毕坦慎则
% find local max/min points
d = diff(h)% approximate derivative %%求各点手敬导数
maxmin = []% to store the optima (min and max without distinction so far)
for i=1:N-2
if d(i)==0% we are on a zero %%导数信陪为0的点,即”驻点“,但驻点不一定都是极值点,如y=x^3的x=0处
if sign(d(i-1))~=sign(d(i+1)) % it is a maximum %%如果驻点两侧的导数异号(如一边正,一边负),那么该点为极值点
maxmin = [maxmin, i]%%找到极值点在信号中的坐标(不分极大值和极小值点)
end
elseif sign(d(i))~=sign(d(i+1)) % we are straddling a zero so%%如y=|x|在x=0处是极值点,但该点倒数不存在,所以不能用上面的判
断方法
maxmin = [maxmin, i+1] % define zero as at i+1 (not i) %%这里提供了另一类极值点的判断方法
end
end
if size(maxmin,2) <2 % then it is the residue %%判断信号是不是已经符合残余分量定义
break
end
% divide maxmin into maxes and mins %% 分离极大值点和极小值点
if maxmin(1)>maxmin(2) % first one is a max not a min
maxes = maxmin(1:2:length(maxmin))
mins = maxmin(2:2:length(maxmin))
else% is the other way around
maxes = maxmin(2:2:length(maxmin))
mins = maxmin(1:2:length(maxmin))
end% make endpoints both maxes and mins
maxes = [1 maxes N]
mins = [1 mins N]
%------------------------------------------------------------------------- % spline interpolate to get max and min envelopesform imf
maxenv = spline(maxes,h(maxes),1:N) %%用样条函数插值拟合所有的极大值点
minenv = spline(mins, h(mins),1:N)%%用样条函数插值拟合所有的极小值点
m = (maxenv + minenv)/2% mean of max and min enveloppes %%求上下包络的均值
prevh = h% copy of the previous value of h before modifying it %%h为分解前的信号
h = h - m% substract mean to h %% 减去包络均值
% calculate standard deviation
eps = 0.0000001% to avoid zero values
SD = sum ( ((prevh - h).^2) ./ (prevh.^2 + eps) )%% 计算停止准则
end
imf = [imfh]% store the extracted IMF in the matrix imf
% if size(maxmin,2)<2, then h is the residue
% stop criterion of the algo. if we reach the end before n
if size(maxmin,2) <2
break
end
c = c - h% substract the extracted IMF from the signal
end
return
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