A basis B of a vector space V is a subset B of V, such that the elements of B are linearly independent and span V. That is to say, every element (vector) of V is a linear combination of elements of B, and no element of B is a linear combination of the other elements of B. Moreover, every basis determines a unique decomposition of any member of V into coordinates relative to B.
This post gives a simple Haskell implementation for a canonical basis of a vector space, and a means of decomposing vectors into coordinates. It uses [indexed type families] (associated types), and is quite general, despite its simplicity.
The Haskell module described here is part of the vector-space library (version 0.4 or later), which available on Hackage and a darcs repository. See the wiki page, interface documentation, and source code. The library version described below (0.5 or later) relies on ghc 6.10.
- 2008-11-09: Tweaked comment above about version.
- 2008-02-09: just fiddling around