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Re: [Groff] Why does tty-char.tmac not represent meaning?
From: |
Ingo Schwarze |
Subject: |
Re: [Groff] Why does tty-char.tmac not represent meaning? |
Date: |
Sun, 25 Jun 2017 02:40:52 +0200 |
User-agent: |
Mutt/1.6.2 (2016-07-01) |
Hi Doug,
thanks for commenting, also showing that you are not opposed to the
general idea.
Doug McIlroy wrote on Sat, Jun 24, 2017 at 07:22:11PM -0400:
> Please change "gradient" to a generic name.
> It is usually read "del"
Using that designation would be unfortunate because "del" is also
commonly used for the partial derivative symbol, round d, \(pd.
> or "nabla"
I'm certainly fine with "nabla"!
> and it is often symbolized "grad" or "div"
I wouldn't like "div"; in tensor analysis, "div" == \(gr\(pc
is not the same as "grad" == \(gr; the latter is a vector
operator taking a scalar argument (or increasing the order
of the tensor it operates on when using the tensor product),
while the former is a linear form (or decreasing the order
of the tensor it operates on).
> But "gradient", by picking out one meaning of several
> (gradient, divergence, laplacian)
I have never seen the "nabla" symbol used for "laplacian".
The Laplacian is the scalar product of the gradient with
itself, or equivalently, the divergence of the gradient.
The Laplacian is a scalar, while both "grad" and "div" are
first order tensors.
So, for the Laplacian, we have
\(*D = \(gr \(pc \(gr
but the "nabla" symbol itself is never called "laplacian"
as far as i can tell.
> can obscure, rather than reveal, the meaning.
Indeed, arguably, pronouncing
grad s = \(gr s
div v = \(gr \(pc v
curl v = \(gr \(mu v
lapl s = \(gr \(pc \(gr s
as
grad s = nabla s
div v = nabla dot v
curl v = nabla cross v
lapl s = nabla dot nabla s
can be considered more natural and less likely
to cause misunderstandings than
grad s = gradient s
div v = gradient dot v
curl v = gradient cross v
lapl s = gradient dot gradient s
though i did certainly hear both in spoken language.
Anyway, it would be nice to get the patch in!
Individual characters can always be reviewed and tweaked on a
case-by-case basis once the general policy is established.
Yours,
Ingo