[Numpy-discussion] untenable matrix behavior in SVN
Gael Varoquaux
gael.varoquaux@normalesup....
Tue Apr 29 14:30:59 CDT 2008
On Tue, Apr 29, 2008 at 12:22:18PM -0700, Timothy Hochberg wrote:
> First, there seems to be disagreement about what a row_vector and
> column_vector are (and even if they are sensible concepts, but let's leave
> that aside for moment). One school of thought is that they are
> one-dimensional objects that have some orientation (hence row/column).
> They correspond, more or less, to covariant and contravariant tensors,
> although I can never recall which is which. The second view, which I
> suspect is influenced by MatLab and its ilk, is that they are
> 2-dimensional 1xN and Nx1 arrays. It's my view that the pseudo tensor
> approach is more powerful, but it does require some metainformation be
> added to the array. This metadata can either take the form of making the
> different objects different classes, which leads to the matrix/row/column
> formulation, or adding some sort of tag to the array object (proposal #5,
> which so far lacks any detail).
Good summary. I support the 1D object with orientation, rather than the
2D object with special indexing. I would call the
row_vector/column_vectors bras and kets rather than tensors, but that
because I come from a quantum mechanics background.
> Second, most of the stuff that we have been discussing so far is primarily
> about notational convenience. However, there is matrix related stuff that
> is at best poorly supported now, namely operations on stacks of arrays (or
> vectors). As a concrete example, I at times need to work with stacks of
> small matrices. If I do the operations one by one, the overhead is
> prohibitive, however, most of that overhead can be avoided. For example, I
> rewrote some of the linalg routines to work on stacks of matrices and
> inverse is seven times faster for a 100x10x10 array (a stack of 100 10x10
> matrices) when operating on a stack than when operating on the matrices
> one at a time. This is a result of sharing the setup overhead, the C
> routines that called are the same in either case.
Good point. Do you have an idea to move away from this problem?
Gaël
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