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

### vinod kumar govindu (view profile)

on 20 Jan 2017
Latest activity Edited by David J. Mack

### David J. Mack (view profile)

on 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.

on 20 Jan 2017
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

### vinod kumar govindu (view profile)

on 20 Jan 2017
what we have to do for getting response at negative lags also? I am new to the matlab and dsp.

### David J. Mack (view profile)

on 20 Jan 2017
Edited by David J. Mack

### David J. Mack (view profile)

on 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