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data structure design question

Felix Thibault felixt at dicksonstreet.com
Sun Feb 20 20:36:03 EST 2000 
At 14:02 2/17/00 GMT, Michael Zawrotny wrote:
>On 17 Feb 2000 08:45:10 GMT, Thomas Hamelryck <thamelry at vub.ac.be> wrote:
<Thomas explains that a graph is good for storing the connectivity
 of a molecule, but I need another way to store bond information.
 He mentions the approach used by X-PLOR, associating types with
 atoms and looking up information on bonds between atoms of a
 certain type in a dictionary.>

 <Michael points out that  X-PLOR requires 
  different atom types for e.g. the sp2 carbons in ethylene
  and formaldehyde and if I don't need this level of detail
  I could start out with just types for sp, sp2 and sp3 and
  get most of the geometry without an explosion in atom types>


What I want to model is an oscillating reaction (the Belousov=
Zhabotinsky reaction) and I had a scheme like this in mind:

class Atom(QNode):
	....
class Molecule(QGraph):
	Node = Atom
	....
class Solute(Molecule):
	def __init__(self, concentration, *substargs):
		self.conc = concentration
		apply(Substance.__init__, (self,)+substargs)
	....
class Solvent(Molecule):
	def __init__(self, fraction, *substargs):
		self.frac = fraction
		apply(Substance.__init__, (self,)+substargs)
	....
class Solution:
	def __init__(self, solvents, solutes, volume):
		"""set initial concentrations"""
	def reaction1(self):
		"""use rate law to get changes in concentration"""
	....
	def react(self, iterations, step=1):
		"""run all reactions and update concentrations, every
		step iterations, store concentrations in the return 		value"""

So, to begin with, the Molecule objects would just do a few things,
like calculate their molecular mass, and the meat of the module would
be in the reaction methods. I was thinking, though, that if I chose
the right data structure for the molecules to begin with, it would be
easier to do more at lower levels, later, or to drop in something like
MMTK, that would make the Molecules behave so that the reactions were
more...automatic. Well, that's probably asking a little too much :)

But right now, I'm looking at graphs made of these:

class QNode:
    """QNode -> nodes which keep a count of how many times they are linked
       """
    def __repr__(self):
        return self._name + `self._index`
    def __init__(self, name, index):
        self._name = name
        self._index = index
        self.links = {}
    def link(self, other):
        """link(other) Set to one/increment link count to node"""
        self.links[other] = self.links.get(other, 0) + 1
    def delink(self, other):
        """delink(other) Decrement/delete link count to node"""
        self.links[other] = self.links.get(other, 1) - 1
        if not self.links[other]:
            del self.links[other]

...but maybe there's something I'm not getting and it's a Bad Idea
for nodes to carry bond order ?
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