decimeter

[SteenGroðe]

I have kind of lost track on what I have been doing to the unit system and what Mathsoft has done. At the moment I can't figure out who at some point has added decimeter to the system (it isn't present i v14). Has Mathsoft at some point had decimeter in the unitsystem or is it just me?

Steen Gro�e

[PhilipOakley]

V11.2a Enterprise doesn't have it listed in the insert units dialog.

dm is used a lot by those in optics because as a numeric value, a radius and a curvature (1/r), in dm, have similar natural values centred on 1.0

Philip Oakley

[RichardJ]

On 5/1/2008 4:43:17 AM, philipoakley wrote:

>dm is used a lot by those in
>optics because as a numeric
>value, a radius and a
>curvature (1/r), in dm, have
>similar natural values centred
>on 1.0

??. r=1/r when r=1xxx for any unit xxx, including parsecs and Smoots.

I hadn't noticed that they had added the Smoot (living close to Boston, a unit I am actually quite familiar with). There are a few other really useful units that we are missing:

http://en.wikipedia.org/wiki/List_of_humorous_units_of_measurement

They should at least add Barn-megaparsec and Donkeypower!

Richard

[StuartBruff]

On 5/1/2008 9:06:34 AM, rijackson wrote:

I have asked for the Potrzebie System of Units to be added - I think I used it as an example on a worksheet I sent to Leslie.



> and Donkeypower!

Presumably they don't want to make asses of themselves? OTOH, maybe they could sell a copy to Shrek.

Stuart

[PhilipOakley]

On 5/1/2008 9:06:34 AM, rijackson wrote:
>On 5/1/2008 4:43:17 AM, philipoakley
>wrote:
>
>>dm is used a lot by those in
>>optics because as a numeric
>>value, a radius and a
>>curvature (1/r), in dm, have
>>similar natural values centred
>>on 1.0
>
>??. r=1/r when r=1xxx for any unit xxx,
>including parsecs and Smoots.
>
>I hadn't noticed that they had added the
>Smoot (living close to Boston, a unit I
>am actually quite familiar with). There
>are a few other really useful units that
>we are missing:
>
>http://en.wikipedia.org/wiki/List_of_hum
>orous_units_of_measurement
>
>They should at least add Barn-megaparsec
>and Donkeypower!
>
>Richard

Richard,

the point was that the optician 😉 who wrote the FORTRAN design code had lots of values in both length and length^-1.
By choosing the dm he was able to make both sets of data have values near 1.0, rather than say 10 and 0.1 for his typical lens designs.
He wrote some pretty good design codes, and being in-house it was ahead of ZEMAX etc. [had GRIN codes and all sorts]

Philip Oakley

[RichardJ]

On 5/1/2008 10:53:46 AM, philipoakley wrote:

>the point was that the optician 😉 who
>wrote the FORTRAN design code had lots
>of values in both length and length^-1.
>By choosing the dm he was able to make
>both sets of data have values near 1.0,
>rather than say 10 and 0.1 for his
>typical lens designs.

OK. I see what you mean now. Apart from aesthetics I don't see what the benefit of keeping the numbers close to 1 is though.

Richard

[PhilipOakley]

On 5/1/2008 11:14:36 AM, rijackson wrote:
OK.
>I see what you mean now. Apart from
>aesthetics I don't see what the benefit
>of keeping the numbers close to 1 is
>though.

>Richard

He was writing fast lens design code and hidden under all the modern codes is some very compact coding that uses shorter word lengths than you might expect and careful and special approximations that you probably are aware of, given your background.

These special bits of code meant that 'back then' making sure that you avoided overflows and balanced the bit placings meant that numbers near one were good.

They still are for some matrix solvers, so as to avoid needing to normalise, along with simplifying pre-conditioners to get the spectral radii of the right size.

Philip Oakley

[SteenGroðe]

On 5/1/2008 4:43:17 AM, philipoakley wrote:
>V11.2a Enterprise doesn't have
>it listed in the insert units
>dialog.

>Philip Oakley

No, I know that. I better be more specific. Decimeter is not in 11.2 and it is not in 14 (but can be made). Now, I have it in 13.1 but I do not have v12 installed anymore so I can't check that release. My question is very simple: Does anybody else but me have decimeter in their unit system in any version since 11.2?

Steen Gro�e

[RichardJ]

I do not have it in version 11.2, 13.1, or 14.0 M011. I no longer have 12 installed, so I can't check that one.

I think maybe you were playing with the units files?

Richard

[IRstuff]

Ditto Richard's post. No dm anywhere.


TTFN,
Eden

[SteenGroðe]

Okay, it must be my own, thanks.

(now I have learned why I have to document what ever I fool around with)

Steen Gro�e

[TomGutman]

Never mind decimeter. Pedestrian. But where did the Smoot come from?
__________________
� � � � Tom Gutman

[StuartBruff]

On 5/1/2008 5:29:11 AM, Tom_Gutman wrote:
>Never mind decimeter.
>Pedestrian. But where did the
>Smoot come from?
>__________________
>� � � � Tom Gutman

MIT, where a certain Allen Razdow went.

http://en.wikipedia.org/wiki/Smoot

Interestingly, Oliver Smoot was at some point Chairman of the American National Standards Institute (ANSI) and President of the International Organization for Standardization (ISO).

Stuart

[jyripikner]

I put decimeter (dm) in mathcad and it says that this variable is undefined. How can I define it then?

[LucMeekes]

Simply define

dm:=m/10

If you're using Prime, make sure that both dm and m are labelled as Unit.

Success!
Luc

[-MFra-]

Hi,

Mathcad does not provide a multitude of multiples and submultiples of units of measurement. So much so that I, all those I need, I have defined and collected in a file, as you can see in the following picture. The file created in this way can be connected to the file in which you work by inserting the "reference".