Re: Garbage collection problem

• To: mathgroup at smc.vnet.net
• Subject: [mg51965] Re: Garbage collection problem
• From: D Herring <dherring at at.uiuc.dot.edu>
• Date: Fri, 5 Nov 2004 02:20:04 -0500 (EST)
• References: <cm7d0u\$lho\$1@smc.vnet.net> <200411030626.BAA08435@smc.vnet.net> <cmckmc\$i47\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```> That's an odd bug; but I kind of doubt StoppingTest is working well for you ANYWAY.

I don't know what you mean by that...  StoppingTest is a bit awkward to
work with, but I've found ways to manage, and its performing beautifully
- if you can ignore the memory leak.

Essentially, I have a dynamical system that regularly impacts with a
rigid surface.  By setting the StoppingTest to halt NDSolve shortly
*after* the impact has occurred, I can save a lot of simulation time,
and it makes it easier to find the exact impact point.

I'm essentially doing the following:

(* Expect impact around 0.5; but can happen after 2 *)
soln=NDSolve[eqn, vars, {t, 0, 3}, StoppingTest->test];

(* Detect where NDSolve stopped *)
tau=(vars[[1]]/.soln)[[0, 1, 1, 2]]

(* Find the exact surface intersection *)
tImpact=FindRoot[surface/.soln, {t, tau}];

Because of the highly nonlinear behavior of my system, FindRoot won't
converge unless I give it a reasonably good estimate of the intersection
time.  StoppingTest gives me that and stops NDSolve as soon as possible.

If you have any better ideas, I'm all ears.

Thanks,
Daniel

```

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