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From: Lynn McGuire <lynnmcguire5@gmail.com>
Newsgroups: rec.arts.sf.written,rec.arts.comics.strips
Subject: Re: xkcd: Tukey
Date: Sat, 21 Jun 2025 14:20:19 -0500
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On 6/21/2025 3:51 AM, Thomas Koenig wrote:
> Lynn McGuire <lynnmcguire5@gmail.com> schrieb:
>> xkcd: Tukey
>>      https://www.xkcd.com/3104/
> 
> That one is really good, and reminds me of Mark Twain's
> quote about the length of the Missisippi.
> 
>> So true, so true.  I can always tell who is a new user of simulation
>> software, they expect to get 9 (ppb, parts per billion) or 12 (ppt,
>> parts per trillion) digits of precision out of our software.  I will go
>> through my explanation of how simulation software is based on
>> experimental data of 2 or 3 digits of precision and watch their faces
>> change when they start to understand.
> 
> You could also try explaining about the analytics.  If they hand
> you an analysis which is accurate to 9 ppb in one of the main
> components (not a trace component where 9 ppb which, for xome
> reason, can be found at that level and where the 9 ppb is a large
> fraction of what is in there), and prove that it's accurate even
> when two different labs analyze it, several times, and the labs
> don't know they are analyzing the same sample,
> 
> Or the number of theoretical stages in a column - that is a
> model based on a false assumption, but (AFAIK) everybody
> lumps mass transfer and equilibrium together; the HTU/NTU
> method that I also learned at university is not really used,
> and you cannot use a fractional number of theoretical stages.
> 
> But if they are asking for REPRODUCIBILITY, that is a very
> much different matter, and can be quite justified.  (The value
> converged to should be the same up to a certain accuracy for
> different reasonable starting conditions).  They might want to use
> a gradient-based optimization, which requires numerical derivatives,
> for example.

I have eight column models with theoretical stages and four column 
models with actual stages.  It is very confusing to the users.  All of 
them match well to real life if they are tuned well and used properly.

Several of the theoretical stage columns use numerical derivatives.  One 
method that my fellow engineer created while he was teaching at Rice. 
And a couple of methods based on the Boston Inside-Out method.  The 
problem with the numerical derivative methods is that if any feed or 
product stream goes to zero then the method cannot recover from that and 
must move to an alternate solver method.

Lynn