demo7.m

这是一个 York大学开发的FDTD代码。很好用的工具

% uses setup from demo0
disp('Constant cosine-waves - extended window with zero padding')


disp('Generate time and frequency steps')
Ts=Tp/(N)
fs=1/Ts
f=linspace(0,fs*(N-1)/N,N);
fx=linspace(0,fs*(NX-1)/NX,NX);
disp('Generate time steps for one period (t)');
t=linspace(0,Tp*(N-1)/N,N);
tx=linspace(0,NX/N*Tp*(NX-1)/NX,NX);


disp('Generate time sequence (x) and plot it against time (t)')
x=ones(1,size(f0,2))*(cos(2*pi*f0'*t));
x=[x,zeros(1,NX-N)];
%
%disp(' Window x');
%Full Gaussian
%w=exp(-((tx-Tp/2)./(0.2*Tp)).^2);

%Half Gaussian
%w=exp(-(tx./(1*Tp)).^2);

%Integrated Gaussian end
%w0=exp(-((tx-Tp)./(0.1*Tp)).^2);
%plot(tx,w0);
%w=1 - psum(w0)/sum(w0);

%Integrated Gaussian both ends
%kw=0.1;
%w1=exp(-((tx-kw)./(kw*Tp)).^2);
%w0=exp(-((tx-kw)./(kw*Tp)).^2) - exp(-((tx-Tp)./(kw*Tp)).^2);
%plot(tx,w0);
%w=psum(w0)/sum(w1);

%Raised cosine at both ends
kw=0.2
w=[(1-cos(0:pi/(kw*(N)):pi))*0.5,ones(1,N*(1-2*kw)-2),0.5*(1+cos(0:pi/(kw*(N)):pi)),zeros(1,NX-N)];
xlabel('Time')
title('The window function')
plot(tx,w);
input('Any key to continue')

x=x.*w*N/sum(w);
%
title('Cosine waves windowed')
xlabel('Time')
plot(tx,x)
title('Extended time series with window')
input('Any key to continue')

disp('Generate DFT (X) of time series (x) and Compare with Fourier transform of continous data');
XD=2*Ts*fft(x);
XD(1)=0.5*XD(1);
title('Discrete Fourier Transform Spectra (Extending the time series)')
xlabel('Frequency/fs')
ylabel('abs(X)')
semilogy(fx/fs,abs(XD),'-',f0/fs,ones(1,size(f0,2)),'+')