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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Not to incite a language war but apparently the Corona lockdown
 was based on 13 year old undocumented C-Code
Date: Tue, 12 May 2020 23:27:14 +0200
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Date: 2020-05-12T23:27:14+02:00
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On 5/12/20 9:16 PM, Niklas Holsti wrote:
>>
>> It seems clear that the code that was executed to create the predictions was 
>> not deterministic on a single core.
> 
> The first of the two cases of single-core "non-determinism" described and 
> bewailed in the "review" is that the time evolution of the predicted epidemic is 
> different depending on the value of a program option -- whether the "network" is 
> created anew, or reused -- that should not affect the result. No actual 
> non-determinism is claimed in the review, just that the epidemic reaches large 
> infection rates sooner for one option value than for the other. It seems that 
> the code was using the PRN generator slightly differently in the two cases, 
> resulting in different PRN sequences.

The single-core non-determinism that I gathered from the referenced 
interpretation of the review, which I clearly have not studied as carefully as 
you, was that the program gave different results on the same computer for 
identical inputs: same initial conditions and same RNG seed(s). Perhaps I 
misunderstood, but that was what I got from it, and the only part that seemed 
troubling. This is different from the kind of non-determinism of simulations 
that are intended to be run many times with different RNG seeds. Possibly that 
would be caused by accessing uninitialized variables.

-- 
Jeff Carter
"I did not rob a bank. If I'd robbed a bank, everything
would be great. I tried to rob a bank, is what happened,
and they got me."
Take the Money and Run
139