[gmx-users] How does g_msd calculate the deviation of diffusion coefficient?

[Hu Zhongqiao]

Hi,
 
Every time I use g_msd to calculate the MSD for one group, this program
always output the diffusion constant like
 
# D[       SOL] = 0.4996 (+/- 0.0366) (1e-5 cm^2/s)
 
I know that g_msd calculates the D using the least square (LSQ) method.
But I dont know how to calculate the deviation of D. In this case, how
does g_msd get +/- 0.0366?  Although I got the exactly same D value
using LSQ, I failed to reproduce this deviation value. I know maybe it
is very simple, but I have spent considerable time without success. Can
anyone explain how to calculate it from the angle of mathematics so that
I can easily reproduce the deviation of D?
 
Thanks in advance,
 
Zhongqiao Hu
 
National University of Singapore
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