On 10/10/05 4:12 PM, "Matt Calabrese" <rivorus@gmail.com> wrote:
Also note that just like with points and vectors, it generally doesn't make sense to add together two absolute temperatures, whereas it does make sense to subtract two. As well, it even makes sense to add the result of the subtraction to an absolute temperature, and the same goes for all other standard point and vector operations. Finally, just like in geometry, there are a few places where the rules can be broken regarding adding points, such as with barycentric combinations. With temperatures, a barycentric combination could be used to find the average temperature of the day. Just like with temperatures, the geometric representation applies to all other unit types. If users find it difficult to understand, most can get away with just using scalar quantities all of the time, though the more advanced users would recognize the benefits of using points and vectors.
If I recall my physics correctly, your use of temperature as a model is a bad one. It _actually_ does make sense to add temperatures, just like two lengths. That's because zero temperature is an actual zero point, just like zero length. You can't use degrees Celsius or degrees Fahrenheit because they have a built-in offset. You have to use an absolute scale, like Kelvin[1]. Back when thermometers were invented, no one knew enough thermodynamics to realize the existence of an absolute zero, let alone have any technology that can generate temperatures close to that point. If you want a better example, look no further than the main language of this list. (Think "pointers," "offsets," and "array segments.") [1] The "degree" was dropped from "Kelvin" because it's an absolute unit, so math with it works just like "meters" or "kilograms". -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com