Re: Not to incite a language war but apparently the Corona lockdown was based on 13 year old undocumented C-Code

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2020-05-13 16:52, Optikos wrote:
> On Wednesday, May 13, 2020 at 4:36:15 AM UTC-5, Niklas Holsti wrote:
>> On 2020-05-13 1:39, Jeffrey R. Carter wrote:
>>> On 5/13/20 12:20 AM, Niklas Holsti wrote:
>>>>
>>>> I agree that it would be troubling. If you could find that statement,
>>>> it would interest me.
>>>
>>> In https://lockdownsceptics.org/code-review-of-fergusons-model/ it says,
>>> "the code produces critically different results, even for identical
>>> starting seeds and parameters."
>>
>> While the review claims that as a general flaw, it then "illustrates"
>> the claim by discussing the two cases I detailed, in particular the
>> unexpected influence of the option controlling how the program "stores
>> data tables". This was eventually traced to a difference in the way the
>> program used the RNG, depending on this option, which then led to
>> different PRN sequences, depending on this option. An error in the
>> program, of course, but not non-determinism.
>>
>> For programs that use RNGs to drive simulations, a single extra RNG
>> call, or a single omitted RNG call, will completely change the
>> subsequent PRN sequence. This has no effect on the statistical
>> properties of the results from many runs, but will of course change the
>> results of the particular run in which the change occurs.
>>
>>> Initially it was claimed that this was
>>> only true for multiple cores, but later that was retracted: "But
>>> Edinburgh came back and reported that – even in single-threaded mode –
>>> they still see the problem."
>>
>> It seems that some users (Edinburgh) reported that the results varied,
>> and reported they were using multi-core mode. The authors of the program
>> (Imperial) replied that result variations are expected in multi-core
>> mode; this was of course a sloppy analysis of the problem, but not an
>> unnatural one. When the users reported that the problem occurs also in
>> single-core mode, depending on the "data table storage" option, the
>> authors found and fixed the error.
> 
> On which date did they fix the problem?  Before or after governments
> acted on the miscalculations?

There has been no demonstration that the early predictions from this 
program, that prodded governments into action, were "miscalculations" to 
any significant degree, especially after the recommended practice of 
performing several runs and considering the ensemble of results.

The single comparison reported in the "second review" between the 
current version and the earliest accessible version of the program 
showed results that were similar in their degree of horror. Even the 
milder result should have caused drastic action, IMO.

-- 
Niklas Holsti
niklas holsti tidorum fi
       .      @       .