xkcd: Tukey
https://www.xkcd.com/3104/

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.

Explained at:
https://www.explainxkcd.com/wiki/index.php/3104:_Tukey

Lynn


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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.

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On Fri, 20 Jun 2025 17:56:59 -0500, Lynn McGuire
<lynnmcguire5@gmail.com> wrote:

xkcd: Tukey
https://www.xkcd.com/3104/

So true, so true. I can always tell who is a new user of simulation=20 >software, they expect to get 9 (ppb, parts per billion) or 12 (ppt,=20
parts per trillion) digits of precision out of our software. I will go=20 >through my explanation of how simulation software is based on=20
experimental data of 2 or 3 digits of precision and watch their faces=20 >change when they start to understand.

Explained at:
https://www.explainxkcd.com/wiki/index.php/3104:_Tukey

Of course they can get 9ppb out. Computers have no problem computing
on and on if you let them. It's just that everything after the second
decimal digit (or whatever the value for the answer is) will be
garbage.

These are the people the <https://en.wikipedia.org/wiki/Blinkenlights>
posters were meant to address.
--=20
"Here lies the Tuscan poet Aretino,
Who evil spoke of everyone but God,
Giving as his excuse, 'I never knew him.'"

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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


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Lynn McGuire wrote:

xkcd: Tukey
ÿÿ https://www.xkcd.com/3104/

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.ÿ 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 get them to understand?

Could you try with policy makers?

Yes, yes, I know you're going to laugh again. This time with ample justification!

William Hyde


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On 6/21/2025 3:09 PM, William Hyde wrote:

Lynn McGuire wrote:

xkcd: Tukey
ÿÿÿ https://www.xkcd.com/3104/

So true, so trueÿÿ 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.ÿ 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 get them to understand?

Could you try with policy makers?

Yes, yes, I know you're going to laugh again.ÿ This time with ample justification!

William Hyde

The worst thing is getting the young inexperienced engineers to
understand that even though we are first principles simulation software,
they think that any simulation is good for making billion dollar
decisions on. They need to validate that simulation with a pilot plant
and extreme laboratory data first. Few do nowadays.

Lynn


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Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

The worst thing is getting the young inexperienced engineers to
understand that even though we are first principles simulation software, they think that any simulation is good for making billion dollar
decisions on. They need to validate that simulation with a pilot plant
and extreme laboratory data first. Few do nowadays.

Judging the quality particular model is definitely part of the
art of engineering; judging if errors are on the safe side or
not also plays a large role.

A colleague of mine once stated, ironically, "Convergence means
correct", which has become a favorite quip in our group.

If I were to write a new simulation program from scratch, (which
I'm not), I would probably include sensitivity analysis into the
model right from the start, so people can now (if they care to know)
how a difference in composition, temperatre, pressure or material
properties will affect their results. This could also provide a
guideline to those young engineers where the problems are.

Plus (as much as this pains me to say, as you know I'm a Fortran
person) I would probably build this package on Julia, which can do autodifferentiation and analytic Jacobians right out of the box,
has cool ODE solvers and is reasonably fast because functions
are compiled.

Maybe a little anecdote: Once upon a time, some people wanted to
build a distillation column. The did the calculation using the
material properties provided by a well-known simulation package.
Somebody noted that things were a little too close for comfort
to an azeotrope, and asked the thermodynamics people to do some
measurements to confirm the design. The thermodynamics people
measured and found that the azeotrope was indeed much closer than
previously calculated, and that the column actually needed a factor
of four more theoretical stages than been originally simulated.
The column started up on time and delivered in-spec product.

They caught this in time, but less experienced engineers might
not have, and sensitivity analysis could have pointed a less
experienced engineer into the right direction.

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Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

On 6/21/2025 3:51 AM, Thomas Koenig wrote:

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.

[...]

Several of the theoretical stage columns use numerical derivatives. One method that my fellow engineer created while he was teaching at Rice.

What I meant was the the results were reproduceble (and smooth)
enough so they could be used in an external gradient-based method
of optimization.

And a couple of methods based on the Boston Inside-Out method.

That must be a reference to Henry Morgan's "Boston Inside Out! Sins
of a Great City!", right? :-) (Actually, I know what it is).

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Lynn McGuire wrote:

On 6/21/2025 3:09 PM, William Hyde wrote:

Lynn McGuire wrote:

xkcd: Tukey
ÿÿÿ https://www.xkcd.com/3104/

So true, so trueÿÿ 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.ÿ 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 get them to understand?

Could you try with policy makers?

Yes, yes, I know you're going to laugh again.ÿ This time with ample
justification!

William Hyde

The worst thing is getting the young inexperienced engineers to
understand that even though we are first principles simulation software, they think that any simulation is good for making billion dollar
decisions on.ÿ They need to validate that simulation with a pilot plant
and extreme laboratory data first.ÿ Few do nowadays.

In terms of policy I was thinking of a bridge built up here across a
cold saltwater strait.

It was clear (from previous work done) that the supports of the bridge
were sturdy enough to resist sea ice, and far enough apart to prevent a
dam of sea ice from building up.

Nonetheless a sea ice model was run to test the latter conclusion. The problem was, that although it was a good model for predicting large
scale changes in sea ice, it was utterly inappropriate for the current
problem (a crowbar is a useful tool, but doesn't work so well as a needle).

The consulting firm got the model from some academics for nothing, and doubtless charged at least five figures for using it.

The bridge is fine, but the waste of time and money was unnecessary, and obviously so.

William Hyde

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