%Generates white nosie and the associates periodogram

clear;

N=400; 
t=1:N;
x=randn(N,1); 

for ct=1:N;
  Nyq(ct)=(-1)^ct; 
end;


figure(1); clf; 
subplot(211); hold on; 
plot(t,zeros(N,1),'k--'); 
plot(t,x,'r'); 
h=ylabel('white noise'); font(h,16); 
h=xlabel('time'); font(h,16); 
font(gca,16); 

subplot(212); hold on; 
[s P]=fftPH(x,1,[]);
s=[0 s 1/(2*diff(t(1:2)))];
P=2*[(1/N*sum(x))^2 P (1/N*sum(Nyq'.*x))^2]; 
plot(s,4*ones(N/2+1,1)/N,'k--'); 
plot(s,P,'r'); 
h=ylabel('squared Fourier coefficients'); font(h,16); 
h=xlabel('frequency'); font(h,16); 
font(gca,16); 

[4/N mean(P)],