Re: What if computation is unrepeatable?

From: Jesse Mazer <lasermazer.domain.name.hidden>
Date: Mon, 11 Jul 2005 17:27:33 -0400

Eugen Leitl wrote:
>
>On Mon, Jul 11, 2005 at 04:45:21PM -0400, Jesse Mazer wrote:
>
> > I don't think that paper is talking about computations being
> > nonrepeatable--they say that they're not talking about "stochastic
> > variations" (which I think refers to genuine physical sources of
> > randomness), but instead about some type of deterministic chaos. Since
>it's
> > deterministic, presumably that means if you feed exactly the same input
>to
> > exactly the same program it will give the same results, the "sensibility
>to
>
>It is quite common that even different compiler optimization flags
>(nevermind
>different architectures) result in
>very different trajectories in numerical simulation (e.g. MD is very
>susceptible to a nonlinear/butterfly effect).

I don't know what compiler optimization flags are, but if the trajectories
are different, presumably that means that you are not really running exactly
the same algorithm, if you include the compiler as part of the whole
algorithm (ie if you wanted to emulate what the computer is doing using a
universal Turing machine, the input strings would have to be different for
different compilers).

Jesse
Received on Mon Jul 11 2005 - 17:29:11 PDT