[gmx-developers] Cubic splines - again

[David van der Spoel]

Mathias PUETZ wrote:
> 
> Hi,
> 
> I also have a question about the cubic spline formula used for 
> potentials and forces:
> 
> As I understand it the spline formula employed by GROMACS enforces that
> potentials and their second derivates are continuous at the tables sites,
> but the first derivates, hence the forces computed from the tables, are 
> not.
> There is always a small discontinuity at the table sites for the first 
> derivatives and therefore the forces.
> I stumbled a across this when I used Eric's kernel tester for BlueGene 
> optimizations.
> 
> I guess my question is: Do you really want a spline formula that makes 
> the forces discontinous ?
> Wouldn't it actually make more sense to use a spline formulat that 
> forces the potential and
> its first derivate to be continuous ? What's the rationale behind making 
> the second derivate
> continuous anyway ?

what makes you think the forces are not continuous?


> 
> Viele Grüsse / Best regards,
> Dr. Mathias Pütz
> 
> IT Specialist for Application Perfomance
> 
> Deep Computing - Strategic Growth BusinessDeep
> IBM Systems & Technology Group
> 
> e-mail:  mpuetz at de.ibm.com
> mobile: + 49-(0)160-7120602
> fax:         + 49-(0)6131-84-6660
> 
> snailmail:
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> 
> 
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-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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