In C++ sence - yes, it's a different point. In mathematical sense, point-point depends on how this operation is defined in your particular space, and in Euclidean space, the result of this operations is the same as difference of corresponding vectors. MW> Yes. But the result is a *vector*. IOW, the difference between 2 MW> points is a mapping from two points in Euclidean space to a vector in MW> a vector space: MW> difference :: E^n x E^n -> R^n I just do not get this. Why would you have a difference between two
MW> The word I was looking for is "Ortsvektor" in German, the vector from MW> the origin to a certain point. What would be the proper word for that MW> in English (tried googling, failed :)? I do now know any other english term for that except for a "vector", but I am not a native english speaker as well. MW> The Euclidean space is E^3, the vector space is R^3. MW> Please see: http://www.ma.umist.ac.uk/kd/curves/node3.html MW> Note also: "Not all books make this distinction so you need to be MW> prepared to encounter the unstated identification E^3 = R^n" MW> Mathworld is using this _unstated_ _identification_; it is imprecise at least. It's not just Mathworld, it's thousands of books/articles. In any case, don't we assume, the gui library will use R^2 space? points in E^n defined as a point in R^n? Valentin Samko http://val.samko.info