Re: [boost] Boost Units library preview
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Matthias Troyer Sent: Saturday, August 19, 2006 1:55 AM To: boost@lists.boost.org Subject: Re: [boost] Boost Units library preview
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If I understand the above concepts correctly then we only need three terms:
- named unit - unnamed unit - quantity (value + unit)
I try to keep the definitions as simple as possible. IMHO, there are really only four distinct concepts: dimension - an "abstract" type quantity - an "abstract" object whose "type" is a dimension unit - a type "derived" from a particular dimension measure - an arithmetic object whose "type" is a unit The last term is a term I introduced to distinguish an object with a dimension from an object with a unit. Very important distinction. Eric.
On Aug 22, 2006, at 1:43 AM, Eric Lemings wrote:
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Matthias Troyer Sent: Saturday, August 19, 2006 1:55 AM To: boost@lists.boost.org Subject: Re: [boost] Boost Units library preview
...
If I understand the above concepts correctly then we only need three terms:
- named unit - unnamed unit - quantity (value + unit)
I try to keep the definitions as simple as possible. IMHO, there are really only four distinct concepts:
dimension - an "abstract" type quantity - an "abstract" object whose "type" is a dimension unit - a type "derived" from a particular dimension measure - an arithmetic object whose "type" is a unit
The last term is a term I introduced to distinguish an object with a dimension from an object with a unit. Very important distinction.
Eric.
Let me check if I understand this correctly in one example. - Nm would be a "dimension" - 1 Nm would be a "quantity" - a torque measured in Nm or an energy measured in Nm would be two distinct units - 1 Nm as torque, 1 Nm as energy or 1 J as energy would be three distinct measures If that is correct then I have several comments, but please check my understanding first. Matthias
On 2006-08-23, Matthias Troyer <troyer@itp.phys.ethz.ch> wrote:
- Nm would be a "dimension"
Not really. It is the unit. The dimension is: MASS * LENGTH^2 * TIME^2
- 1 Nm would be a "quantity" - a torque measured in Nm or an energy measured in Nm would be two distinct units - 1 Nm as torque, 1 Nm as energy or 1 J as energy would be three distinct measures
I think as far as a dimensionality checking goes, they are all the same. As far as a units checking goes, Nm and J *could* be distinguished. It's an interesting question as to what, exactly, "energy" and "torque" are once you try to separate away the dimensionality and units bits... :-) phil -- change name before "@" to "phil" for email
"Phil Richards" <news@derived-software.ltd.uk> wrote in message news:20060823145751.6C0A0AABB8@derisoft.derived-software.demon.co.uk...
On 2006-08-23, Matthias Troyer <troyer@itp.phys.ethz.ch> wrote:
- Nm would be a "dimension"
Not really. It is the unit. The dimension is: MASS * LENGTH^2 * TIME^2
- 1 Nm would be a "quantity" - a torque measured in Nm or an energy measured in Nm would be two distinct units - 1 Nm as torque, 1 Nm as energy or 1 J as energy would be three distinct measures
I think as far as a dimensionality checking goes, they are all the same. As far as a units checking goes, Nm and J *could* be distinguished. It's an interesting question as to what, exactly, "energy" and "torque" are once you try to separate away the dimensionality and units bits... :-)
FWIW If I use a hefty spanner to undo a rusty bolt, then the bolt heats up as I unscrew it. I guess the heat energy gained by the bolt is directly equivalent to the torque I had to apply to undo it. OTOH therefore one would think that applying heat to a rusty bolt should make it unscrew itself but unfortunately for some reason I have never been able to get that to work ! ;-) regards Andy Little
Phil Richards <news@derived-software.ltd.uk> writes:
On 2006-08-23, Matthias Troyer <troyer@itp.phys.ethz.ch> wrote:
- Nm would be a "dimension"
Not really. It is the unit. The dimension is: MASS * LENGTH^2 * TIME^2
Matthias is just trying to understand the way Eric is using the terminology. -- Dave Abrahams Boost Consulting www.boost-consulting.com
participants (5)
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Andy Little -
David Abrahams -
Eric Lemings -
Matthias Troyer -
Phil Richards