Hello, Does anyone know exactly how g_analyze -ac calculates autocorrelation function? My input file, dist.xvg, contains a distance d(t) between two specific atoms of my molecule in time t. (hence d(t)>0) I calculated the autocorrelation function using the following command:
g_analyze -f dist.xvg -ac corr-dist.xvg What I don't understand is that the correlation function C(k) in the output file, corr-dis.xvg, includes some negative values and even goes down to almost -0.5! I thought by definition the autocorrelation function C(t) is calculated as following: C(k) = <d(t)*d(t+k)> where C(k) should be always positive because d(t), distance, is always positive in this case. So does anybody know precisely what formula "g_analyze -ac" uses to calculate the autocorrelation function? Thank you very much for your help in advance. Regards, Sung _______________________________________________ gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users Please search the archive at http://www.gromacs.org/search before posting! Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. Can't post? Read http://www.gromacs.org/mailing_lists/users.php
