[Numpy-discussion] matrix indexing question

[Bill Spotz]

It seems to me that using shapes, (m,1) versus (1,n), to determine  
whether a vector is column- or row-oriented is a hack (or at least  
feels like one).  If we know we have a vector, then we want to use a  
single index to obtain a scalar, and that extra "0," or ",0"  
shouldn't be necessary.

It also seems to me that there is an object-oriented design solution  
to this, namely defining column_vector and row_vector classes that  
inherit from matrix, that accept a single index, but behave as  
matrices consistent with their type.  I'm sure there are implications  
to this I haven't thought through yet, but at least it gives us  
logical indexing AND persistence of matrices through operations.

On Mar 27, 2007, at 1:11 PM, Travis Oliphant wrote:

> Thanks for listing your points.   I can see that this is an issue  
> where
> reasonable people will disagree because there are multiple ways of
> looking at it.
>
> The idea that matrix selection would return matrices really comes from
> wanting to keep matrices more persistent through operations.
>
> M[0]  could be seen either as a 1xn matrix or a n-length array.   I
> agree that both concepts are possible.  Seeing it as a 1xn matrix  
> allows
> matrices to remain persistent more often.
>
> So, the arguments for the current approach and the arguments  
> against it
> to me seem on the same level, so I don't see a reason to change the
> current behavior and see a lot of strong reasons not to change the
> behavior (we are in a 1.0 release and could not change anything  
> until at
> least 1.1 anyway).
>
> With that said:
>
> One of my goals for the next year or two is to create a matrix  
> class in
> C and incorporate CVXOPT matrices and it's coupled sparse  
> matrix.    We
> can re-visit this question in that process.  I would like for there to
> be a sparse matrix implementation in NumPy (without the solver which
> will remain in SciPy).
>
> But, the sparse matrix and the matrix need to have the same behaviors
> and should be able to interoperate with each other.
>
> So, if you would like to help with that project all input is welcome.

** Bill Spotz                                              **
** Sandia National Laboratories  Voice: (505)845-0170      **
** P.O. Box 5800                 Fax:   (505)284-5451      **
** Albuquerque, NM 87185-0370    Email: wfspotz at sandia.gov **