[gmx-users] least-squares fit

[Nguyen Hoang Phuong]

On 18 Oct 2002, David wrote:

> On Fri, 2002-10-18 at 17:11, Nguyen Hoang Phuong wrote:
> > 
> > Dear All,
> > 
> > I have one question concerning to the least-squares fit in GROMACS:
> > 
> > suppose I have two structures obtained at the time t=0 and t=T with set of
> > the coordinates of atoms {r_n} and {R_n}, respectively. I have done as the
> > following: I fit the structure {R_n} to {r_n} and calculate the
> > quantities: delta_r = R'_n - {r_n} where {R'_n} are the coordinates
> > obtained after fitting. 
> > 
> > Next, I fit the structure {r_n} to {R_n} and calculate the 
> > quantities: delta_r' = r'_n - {R_n} where {r'_n} are the coordinates 
> > obtained after fitting.
> > 
> > The result is that delta_r differs delta_r'. According to the
> > least-squares fit method, the two results must be the same. Does anyone
> > know what the reason is? Thanks a lot in advance.
> 
> Are you sure? I tried it using g_confrms -f1 X.pdb -f2 Y.pdb and the
> other way around. I get exactly the same results (6 digits). How large
> is the discrepancy in your case?

after 4th digits.

> > 
> > Regards,
> > 
> > Phuong
> > 
> > 
> > 
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> -- 
> 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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