Matthias Schabel schrieb: [Snip]
How do we convert 32 degrees Fahrenheit to Kelvin? [Snip] Absolute temperature (K) = (Absolute temperature (F) - 32)*5/9 +273.15
However, if we're talking about temperature differences (vectors), then the correct expression is
Temperature difference (K) = Temperature difference (F)*5/9 [Snip]
Hi Matthias, I had a similar problem to distinguish between coordinate systems starting to count at one and those starting to count at zero (which is the standard case). Here is my (very simple) solution: template<class T, unsigned int D> class coord { // a coordinate is a dimension starting to count at 1 T v; public: coord(euclid::dim<T, D> d) : v(d()+1) {} coord(T v0): v( v0>0 ? v0 : 1 ) {} coord(const coord &v0) : v(v0.v) {} coord& operator=(const coord &v0) { v = v0.v; return *this; } euclid::dim<T, D> operator ()() { return euclid::dim<T, D>(v-1); } }; It's intentionally that you can't do anything with a non standard coordinate but transform it into the standard representation (i.e. a dimension). I just couldn't think of any other meaningful operation. Both coordinate systems are technically different vector spaces. Both describe the same points in space, but the vector operations lead to different results when interpreted back into the real world. It seems, only the standard representation can be interpreted in a meaningful way. I think it's the same thing with different temperature units. Each unit defines its own (in this case one-dimensional) vector space. You can add Kelvin to Kelvin and Celsius to Celsius, but you can't mix them. The corresponding results are either in Kelvin or in Celsius respectively and are mathematically two different things. The same applies to differences. That they have the same physical interpretation is rather a coincident. 293.15 Kelvin represent the same temperature as 20 degrees Celsius, but doubling both will lead to very different results. It's up to the user to decide, what 'doubling a temperatures' is supposed to mean in the real world and pick a vector space, i.e. a unit, accordingly; be it Kelvin, Celsius, Fahrenheit or something entirely different. So I'd stick to offer a transformation between absolute temperatures. Differences are meaningful only within a particular vector space. Theoretically you could introduce a notation of a norm, that would be origin invariant but depending on the scale. So Kelvin and Celsius would have the same norm while the norm of Fahrenheit needs to be scaled by 5/9. This, however, is probably much to much hassle. Greetings, Andreas