# Autocorrelation Computation with MATLAB

I have done the computation of the autocorrelation of a sequence (vector), here called "frame", and I have plotted it. Here the code:

The resulting graph is:

I do not understand the position of the peak in this graph: I know that the peak of the autocorrelation should be in the origin, why is it there?

r, lag = xcorr(frame, frame);