any one help me that i find the psd of the random signal having lenght 1000,i write the code but get some error in the result not find correct result

close all;clear all;clc;
n=1000;
m=50;
x=0;
%%%%%%%%random signal
sig=[rand(1,n)-(1/2)];
 sig1=zeros(1,m+1);
for i=1:m+1 
    for j=1:(n-i)+1
         x=x+(sig(j).*sig(j+i-1) );
    end
     x=x/(n-m);
         sig1(i)=x;
end
out=autocorr(sig,m+1);%using built in function of autocorrelation
figure(1);
subplot(2,1,1); 
plot(sig1)
subplot(2,1,2);
plot(out);
%%%power-s-density-code%%%
 f=50;
 z=0;
 psd1=zeros(1,m+1);
for q=1:m+1 
    for w=1:m+1
         z=z+(sig1(w).*exp((-i*2*pi*q*w)/((2*m)+1)));
    end
     z=z/(n-m);
         psd1(q)=z;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%find psd by fft shift
final=fftshift(abs(out));
%%%%%%%%%%%%%%%%%%
 figure(2);
 subplot(2,1,1);
 plot(psd1)
 subplot(2,1,2);
 plot(final)

[the cyclist]

It would be really helpful if you could use the "code" button to format your MATLAB code into a more readable format.

Answer 1

[Wayne King]

Hi, I agree with cyclist's comment. I see that you are using autocorr() from the Econometrics Toolbox.

Do you have the Signal Processing Toolbox? You can use spectrum.periodogram to obtain the PSD. I assume in these examples that the sampling rate is 1. Change it accordingly.

fs = 1;
x = randn(1e3,1);
psdest = psd(spectrum.periodogram,x,'NFFT',length(x),'Fs',fs);
plot(psdest);

If you do not have the Signal Processing Toolbox, you can use fft()

figure;
xdft = fft(x);
xdft = (fs/length(x)).*abs(xdft(1:length(x)/2+1)).^2;
xdft(2:end-1) = 2*xdft(2:end-1);
F = 0:fs/length(x):1/2;
plot(F,10*log10(xdft)); grid on;

Wayne