matlab画包络图

    clear all;
    clc;
    close all;
    n=-5000:20:5000;
    N=length(n);
    nt=0:N-1;
    x=120+96*exp(-(n/1500).^2).*cos(2*pi*n/600);
    [up,down]=envelope(x,N,'analytic');
    plot(nt,x,'k',nt,up,'r',nt,down,'g');
    
    
      
      
      
      
      
      
      
      
      
    

    data12_20=csvread('F:\experiment\3-25\12-20.csv',22,0);
    x12_20=data12_20(:,1);
    y12_20=data12_20(:,2);
    z12_20=data12_20(:,3);
    data34_20=csvread('F:\experiment\3-25\34-20.csv',22,0);
    x34_20=data12_20(:,1);
    y34_20=data12_20(:,2);
    z34_20=data12_20(:,3);
    N