MATLAB|绘制曲线包络

别人的绘制曲线包络的程序。

from:http://www.ilovematlab.cn/thread-18145-1-1.html

Mydefinition_envelope(x,y,interpMethod)

程序

function  [up,down]=Mydefinition_envelope(x,y,interpMethod)

%ENVELOPE gets the data of upper and down envelope of the known input (x,y).
%
%   Input parameters:
%    x               the abscissa of the given data
%    y               the ordinate of the given data
%    interpMethod    the interpolation method
%
%   Output parameters:
%    up      the upper envelope, which has the same length as x.
%    down    the down envelope, which has the same length as x.
%
%   See also DIFF INTERP1

%   Designed by: Lei Wang, <WangLeiBox@hotmail.com>, 11-Mar-2003.
%   Last Revision: 21-Mar-2003.
%   Dept. Mechanical & Aerospace Engineering, NC State University.
% $Revision: 1.1 $$Date: 3/21/2003 10:33 AM $

if length(x) ~= length(y)
    error('Two input data should have the same length.');
end

if (nargin < 2)|(nargin > 3),
error('Please see help for INPUT DATA.');
elseif (nargin == 2)
    interpMethod = 'linear';
end


   
% Find the extreme maxim values
% and the corresponding indexes
%----------------------------------------------------
extrMaxValue = y(find(diff(sign(diff(y)))==-2)+1);
extrMaxIndex =   find(diff(sign(diff(y)))==-2)+1;



% Find the extreme minim values
% and the corresponding indexes
%----------------------------------------------------
extrMinValue = y(find(diff(sign(diff(y)))==+2)+1);
extrMinIndex =   find(diff(sign(diff(y)))==+2)+1;



up = extrMaxValue;
up_x = x(extrMaxIndex);

down = extrMinValue;
down_x = x(extrMinIndex);



% Interpolation of the upper/down envelope data
%----------------------------------------------------
up = interp1(up_x,up,x,interpMethod);
down = interp1(down_x,down,x,interpMethod);

用法

clc;

% Load a signal waveform
%--------------------------------------------
N = 100;
fs = 50;
t = ((1:N)/512)';
T0 = 0.01;
f0 = 12.7;
T1 = 0.026;
f1 = 35.8
y = exp(-T0*t) .* 5 .* sin(2*pi * f0*t) + exp(-T1*t).*4.*sin(2*pi*f1*t);
%load data.txt data;
%t = data(:,1); % time series
%y = data(:,2); % signal data
figure(1);
plot(t,y,'b-');
title('The original signal waveform','FontSize',18);



% Call function envelope to
% obtain the envelope data
%--------------------------------------------
[up,down] = envelope(t,y,'linear');



% Show the envelope alone
%--------------------------------------------
figure(2)
plot(t,up); hold on;
plot(t,down);
title('The envelope of the given signal data','FontSize',18);
hold off;



% Show the original signal and its envelope
%--------------------------------------------
figure(3)
plot(t,y,'g-'); hold on;
plot(t,up,'r-.');
plot(t,down,'r-.');
title('The envelope vs the given signal data','FontSize',18);
hold off;