On Jun 18, 2006, at 1:23 AM, Janek Kozicki wrote:
Gerhard Wesp said: (by the date of Thu, 15 Jun 2006 11:39:15 +0200)
On Thu, Jun 15, 2006 at 02:17:38PM +0700, Oleg Abrosimov wrote:
the problem here is that PQS deals with only dimensions, but physical quantities have not only that, they have rank also.
What is the rank of a physical quantity?
good question indeed. I can grasp the idea of that. In fact above quote written by Oleg was a revelation for me. But how to include the concept or "rank" into the library design? Would it boil down to abstract_quantity_id, but with different name?
I'm really not sure if one can hold energy inside a vector (say: vector field of energy), perhaps some physicist here can answer this question. But I'm sure that momentum can be hold as a vector (ie. momentum vector).
Could it possibly mean, that some quantities can be represented as vectors, while representing others as vector doesn't make sense - would it be "rank" then?
As a physicist I am completely baffled and confused. What do you mean by rank of a quantity? Do you mean the size of a vector/matrix? If so, then this is completely orthogonal to a unit library. You can hold any physical quantity inside a vector, or inside a multi_array of arbitrary dimensions. Just consider a finite-difference or finite element representation of a field theory, and you have multi- dimensional arrays of quantities of essentially any unit you can think of. In my opinion thus the "rank" (if I understand what is meant here) is orthogonal to the unit system. The unit is a property of the value type of the container, and the size (or rank) is a property of the container. Matthias