On Aug 20, 2006, at 10:42 AM, Andy Little wrote:
"Janek Kozicki" <janek_listy@wp.pl> wrote in message news:20060819212430.739b0920@absurd...
Andy Little said: (by the date of Sat, 19 Aug 2006 13:03:42 +0100)
In fact there is a 2D and 3d vector in quan so you can do:
quan::some_vect< quan::length:: m > position_a, position_b;
quan::length:: m distance_a_to_b = magnitude(position_b - position_a);
Because of that useage It might get confusing.
I still hold my position that linear algerbra library should not be a part of _two_ separate libraries: Dimensions and Units.
FWIW I brought this up only in relation to magnitude. That said, I have found that being able to write code like the above is a lot of fun, much more so than if I was using doubles to represent lengths. However suddenly you are restricted in what you can do. For example:
double var1= 10; // var1 meters double var2 = 10 ; // var2 represents meters.
var1 *= var2 ; // var1 now represents an area in square meters.
Of course you cant do this with a fixed_quantity:
quan::length::m var1(10); quan::length::m var2(10); var1 *= var2 ; // Error
I would guess that is an unacceptable restriction for many authors of algebra libraries.
Why should this be an unacceptable restriction? All it says is that a quantity with units is not a field, but that is obvious from the start. I can multiply a vector (3m, 2m, 1m) by a factor of 5 but not by a factor of 5m. I see no problem here at all, except if you assume that the element type of a vector is the same type as the scalar factor in your expression.
As far as I am concerned though I am more interested to see what happens if I do play by the rules that are imposed by having strongly typed quantities, but it is kind of difficult to ask everyone to play by these rules, so I am happy to create vector types myself, that work with Quan.
I don't see any reason why a correctly designed linera algebra library should not work with quantities with units
Maybe, if we can get Quan into Boost then we will be in a stronger position and there may then be interest in creating a linear generic algebra library for physical quantities, but I suspect that due to the above kind of issues, there will always be a great divide between a 'raw' linear algebra library and one that is designed to work with physical quantities.
I don't agree. For me there is no such thing as 'raw' linear algebra. All linear algebra concepts work perfectly with quantities with units. matthias