From: "Robert I. Eachus" <rieachus@comcast.net>
Subject: Re: [OT] Hints for an algorithm - avoiding O(n^2)
Date: Fri, 12 Mar 2004 09:29:23 -0500
Date: 2004-03-12T09:29:23-05:00 [thread overview]
Message-ID: <n76dnaYyIaHZVMzdRVn-gw@comcast.com> (raw)
In-Reply-To: <1Yi4c.85891$dP1.243229@newsc.telia.net>
Bj�rn Persson wrote:
> If that were true, the moon would orbit the sun and not the Earth (if we
> ignore the rest of the universe).
Actually it does. If you compute the gravitational force of the Earth
on the Moon, and compare it to the gravitational force of the Sun, the
Sun has a much greater effect. In fact, the orbit of the Moon around
the Sun is everywhere convex.
However, back to the OP's question. The first thing you want to do is
not use brute force, but use Runga-Kutta for each pair of objects. This
makes the calculation about ten times as complex, but gives a much
better fit. Second when two objects are "close" you should do the
Runga-Kutta interpolation much more often. This usually means
calculating the effects of all gravitational attractions on the objects
that are in close proximity more often as well. (You don't have to do
the reverse, because the effect of the two nearby objects on remote
objects will be that of their center of mass.) Of course you also have
to allow for the possibility that there are several objects that are
gravitationally close. The normal way to do this is to, at the end of
every major cycle look at the positions of all the objects, and decide
which ones get the intermediate steps. It is not worth the effort to
work with two pairs instead of four 'close' objects.
--
Robert I. Eachus
"The only thing necessary for the triumph of evil is for good men to do
nothing." --Edmund Burke
next prev parent reply other threads:[~2004-03-12 14:29 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-12 9:15 [OT] Hints for an algorithm - avoiding O(n^2) Jano
2004-03-12 11:06 ` Jean-Pierre Rosen
2004-03-12 12:53 ` Stuart Palin
2004-03-12 12:55 ` Stuart Palin
2004-03-12 13:48 ` Dmitry A. Kazakov
2004-03-17 1:16 ` jtg
2004-03-12 13:30 ` Björn Persson
2004-03-12 13:42 ` James Rogers
2004-03-12 14:29 ` Robert I. Eachus [this message]
2004-03-12 23:44 ` Björn Persson
2004-03-13 15:21 ` Robert I. Eachus
2004-03-14 17:27 ` Jano
2004-03-15 5:34 ` Robert I. Eachus
2004-03-14 17:27 ` Jano
2004-03-13 0:12 ` Wes Groleau
2004-03-17 2:24 ` jtg
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