[Numpy-discussion] matrix wart
Alan G Isaac
Fri Feb 22 08:42:07 CST 2008
>>> On Thu, Feb 21, 2008 at 12:08:32PM -0500, Alan G Isaac
>>>> a matrix behavior that I find bothersome and unnatural::
>>> M = N.mat('1 2;3 4')
On Fri, 22 Feb 2008, Stefan van der Walt apparently wrote:
> Could you explain to me how you'd like this to be fixed? If the
> matrix becomes a container of 1-d arrays, then you can no longer
> expect x[:,0] to return a column vector -- which was one
> of the reasons the matrix class was created. While not
> entirely consistent, one workaround would be to detect
> when a matrix is a "vector", and then do 1-d-like indexing
> on it.
Letting M be a matrix and A=M.A, and i and j are integers.
I would want two principles to be honored.
1. ordinary Python indexing produces unsurprising results,
so that e.g. M returns the first element of the matrix
2. indexing that produces a 2-d array when applied to A
will produce the equivalent matrix when applied to M
There is some tension between these two requirements,
and they do not address your specific example.
Various reconciliations can be imagined.
I believe a nice one can be achieved with
a truly minimal change, as follows.
Let M[i] return a 1d array. (Unsurprising!)
This is a change: a matrix becomes a container
of arrays (e.g., when iterating).
Let M[:,i] and M[i,:] behave as now.
In addition, as a consistency measure, one might
ask that M[i,j] return a 1 x 1 matrix. (This is
of secondary importance, but it follows the
principle that the use of multiple indexes
Right now I'm operating on caffeine instead of sleep,
but that looks right ...
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