[gmx-developers] Cubic splines - again

Mathias PUETZ mpuetz at de.ibm.com
Mon Aug 21 11:00:42 CEST 2006


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 
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 

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 ?

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

  IBM Deutschland GmbH
  Department B458
  Hechtsheimer Str. 2 / Building 12
  55131 Mainz
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