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


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