# how to plot auto correlation and cross correlation function in a single figure?

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vinod kumar govindu am 20 Jan. 2017
Bearbeitet: David J. Mack am 20 Jan. 2017
while plotting the ACf and CCF i didnt get the negative side of Auto correlation fucntion. I am getting only positive side only.
x=sin(2*pi*f/fs*t);
y=cos(2*pi*f/fs*t);
[ACF,Lags,Bounds] = autocorr(x,nLags,nSTDs);
[XCF,Lag,Bound] = crosscorr(x,y,nLags,nSTDs);
plot(Lags,ACF);
hold on
plot(Lag,XCF);
grid on
i getting output like given figure. Help me to get the negative side of the ACF.
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Did you read the help for autocorr?
'The elements of acf correspond to lags 0,1,2,...,numLags. The first element, which corresponds to lag 0, is unity (i.e., acf(1) = 1).'
vinod kumar govindu am 20 Jan. 2017
what we have to do for getting response at negative lags also? I am new to the matlab and dsp.

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### Antworten (1)

David J. Mack am 20 Jan. 2017
Bearbeitet: David J. Mack am 20 Jan. 2017
The negative autocorrelation is the same as the positive as you use the same signal for the correlation. So if you want to pretend there is a negative part:
plot([-Lags(end:-1:1) Lags],[ACF(end:-1:1) ACF]);
Greetings, David
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