[MMTK] Energy evaluation bug?

Adam Hixson chixson@chemdept.chem.ou.edu
Thu, 4 Oct 2001 13:37:07 -0700 (PDT)


Hi all.  Here's an issue:

If I run the following code:

from MMTK import *

universe = load('universe.univ')
bit = Collection()
bath = Collection()

# and then here assign to bit a section of 
# the universe, and assign to bath the
# rest of the universe

universe.energy()
test = universe.energy(subset1=bit) + \
universe.energy(subset1=bath) + universe.energy(\
subset1=bit, subset2=bath)

####################

I find that test != universe.energy().  In other 
words, splitting
the universe into two parts and then calculating 
their respective energies and their interaction
energy yields a different energy than what it 
ought.

I find that the problem seems to be in the electro-
static bit, as when I use the .energyTerms() method
this is the part that does not add up.

This is using an electrostatic cutoff, apparently
the subsets are not yet ready for ewald sums.

I'm using MMTK v2.2b6 and python2.1, and newest to
recent versions of all other required pieces.

I guess my questions is:  where should I start
looking? :)

=====
----
Adam Hixson
Department of Chemistry and Biochemistry
The University of Oklahoma     chixson@chemdept.chem.ou.edu
620 Parrington Oval            hixsonc@yahoo.com
Norman, OK 73069

__________________________________________________
Do You Yahoo!?
NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month.
http://geocities.yahoo.com/ps/info1