wxruby users - Sep 2011 - ruby to solve a physics question

I am trying to solve one of my graduate level physics problems with
ruby...
Here is what I have so far...

a6=0.0
for n1 in -10..10
  for n2 in -10..10
     for n3 in -10..10
       if n1!=0 and n2!=0 and n3!=0
       p=Math.sqrt(n1**2+n2**2+n3**2+n1*n2/1.414+n1*n3/1.41+n2*n3/1.414)
       a6+=(1/p)**6
       end
     end
   end
end
puts a6

What I''ve got here is a 10x10x10 face-centered cubic lattice of atoms.
What I want to do is find this constant a6= sum(1/Pij)**6.  From a
starting point I want the distance to every other atom location point in
the structure, meanwhile inversing and power to the sixth each distance.
Then I want to add all those up.  This should return 14.4????

-- 
Posted via http://www.ruby-forum.com/.

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Am 14.09.2011 02:34, schrieb thiess cunningham:
> I am trying to solve one of my graduate level physics problems
> with ruby...
Hi thiess,

this is the wxRuby mailinglist, related to the wxRuby GUI toolkit.
Your question should better be served on ruby-talk. Go to
http://www.ruby-forum.com/forum/ruby for posting there.
> Here is what I have so far...
> 
> a6=0.0 for n1 in -10..10 for n2 in -10..10 for n3 in -10..10 if
> n1!=0 and n2!=0 and n3!=0 
> p=Math.sqrt(n1**2+n2**2+n3**2+n1*n2/1.414+n1*n3/1.41+n2*n3/1.414) 
> a6+=(1/p)**6 end end end end puts a6
> 
> What I''ve got here is a 10x10x10 face-centered cubic lattice of
> atoms. What I want to do is find this constant a6= sum(1/Pij)**6.
> From a starting point I want the distance to every other atom
> location point in the structure, meanwhile inversing and power to
> the sixth each distance. Then I want to add all those up.  This
> should return 14.4????
> 
I''m by no means someone who has any knowledge on how atom physics
work, but a few notes on your code:

* Don''t use "for" in Ruby. There''s the #each method
that is the
correct idiom for this. And four your specific case you should use:
  -10.upto(10) do |nx| ... end

* The test against zero can be made much more readable with the
Methods Integer#zero? and Integer#nonzero?

* I''m not willing to dig into the giant term you pass to Math.sqrt.
- From a first glance, you might want to have a look at the
Enumerable#inject method, which you can use to easily sum up things
that are computed the same way.

* Be aware that doing math with floating-point numbers is always
dangerous as they''re not exact. The further you continue to compute
with floating-point results you got, the more unprecise your final
result will be. If I remember correctly, this is the industry standard
to blame for this: http://en.wikipedia.org/wiki/IEEE_754-2008

As I noted before, post your question to ruby-talk. It''s not related
to wxRuby in any way.

Vale,
Marvin
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