Salut, On Tuesday 06 July 2004 11:54, Matthias Troyer wrote: [...]
You can now argues, wether this is still a vector, but in physics it is called a vector.
As another theoretical physicist I want to disagree with this
Sorry for beeing unclear. I wanted to say, "in my special problem, it is a vector". I didn't want to claim that in general.
definition. I would call the object with four indices a linear operator, but not a matrix. Matrices for me are representation of linear operators with two indices.
As I said, that's a matter of taste, convention, education and notation, and it's fine with me.
You however point out an important requirement for generic algorithms on vector spaces: they should not require that a vector can be accessed with operator[] and a single subscript, or that once can construct a vector by passing just the size to the constructor. These too narrow requirements of the Iterative Template Library ITL, caused us to introduce the "vector space" concept in the our Iterative Eigenvalue Template Library IETL.
I agree. Best wishes, Peter