[gmx-users] g_energy averages

[David]

On Wed, 2002-07-17 at 20:15, David L. Bostick wrote:
> 
> .. So, if I want to find the standard error in an average value, I just
> take the fluctuation and divide it by sqrt(nsteps)?
> 
> i.e.
> If I get from the energy file
> Energy                      Average       RMSD     Fluct.
> #Surf*SurfTen               147.805    2270.69    2263.84
> 
> and the run was over 250000 steps, the standard error is
> 
> 2263.84/sqrt(250000)
No you should divide by the sqrt of the number of *independent* data
points. For energy, there is a correlation on the order of a few
picoseconds (depends on system). For e.g. the dipole moment of the box
it is usually 10 ps (can be related to Debye relaxation). g_analyze may
help you estimating errors, but it is not trivial...


-- 
Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
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