I think the cross product is typically used to refer to the outer product, while the dot product refers to the inner product.
On Dec 25, 2011, at 2:51 PM, Ted Dunning <[email protected]> wrote: > This is misleading even if not strictly incorrect. In matrix terminology, > outer product is definitely more commonly used. > > On Sun, Dec 25, 2011 at 1:37 PM, Dmitriy Lyubimov <[email protected]> wrote: > >> Hello, >> >> just stumbled on this in vector while looking for outer product operation >> -- >> >> @Override >> public Matrix cross(Vector other) { >> Matrix result = matrixLike(size, other.size()); >> for (int row = 0; row < size; row++) { >> result.assignRow(row, other.times(getQuick(row))); >> } >> return result; >> } >> >> >> It seems this guy computes an outer product, but not cross product ( >> crossprod for vectors =ab sin(theta)n). Seems like a misleading >> naming. >> >> It is probably motivated by R, where tcrossproduct (which is a product >> of matrices, not vectors) is defined as XY' and crossprod which is >> defined X'Y and so in case of cbind(vector) it would constitute either >> dot product or outer product respectively. But i am not sure where R >> is deriving this; and even then it is definitely misleading as R would >> apply this to the world of matrices, not vectors. In vectors cross >> product means something else and i think this may create a confusion >> (it certainly did in my case).. >> >> thanks. >> -Dmitriy >>
