[Numpy-discussion] untenable matrix behavior in SVN

Christopher Barker Chris.Barker@noaa....
Tue Apr 29 17:03:51 CDT 2008


Gael Varoquaux wrote:
> However I would find it nice that, for linear algebra, 
> x[i, :] == x[:, i].T
> 
> This is the kind of behavior I expect, and we won't be getting it with 1D
> arrays.

But you WOULD get it with 1-d row/column objects.

I'm going to try to summarize what I think is clear from the discussion:

1) There are significant problems with the fact that the current matrix 
object does not reduce rank with indexing.

2) people want a "row" or "column" extracted from a matrix to behave 
like a linear algebra object, for example:  M[:,i] * M[i,:] is an matrix

As far as I can see, the ONLY way to satisfy both of these is with a 
row/column object of some sort.

You can get almost there by having M[i] return a 1-d array, while M[:,i] 
and M[i,:] continue to return Matrices, but this gives an asymmetry 
between extracting rows and columns, and, probably more important, breaks:

M[i] == M[i,:]

plus you don't get the benefit of being able to extract a row or column 
and index the result with a scalar.

-Chris


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Christopher Barker, Ph.D.
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