[PYTHON MATRIX-SIG] Default axis

[Carlos Fonseca]

On Sun, 11 Aug 1996, Jim Hugunin wrote:

> ...
> My only problem with this is the concatenation function which I
> personally think should only be implemented along axis 0, though I've
> been convinced this is too limiting.  Having this default to a different

Being able to cleanly concatenate arrays along other axes would indeed be
useful. Otherwise, we'll end up transposing the concatenation of
transposed arrays sooner or later.

> Having this default to a different axis than 0 really bothers me, but
> I suppose I'll get over it.
> 
> Comments are welcome - Jim

Concatenation does seem to be a special case, and there may a reason to
make it the exception. For example,

>>> a
 0  1  2  3
 4  5  6  7
 8  9 10 11
>>> b
0 1 2 3

Since these arrays are aligned in the usual sense (a+b would work),
one would expect concatenate((a,b)) to work by default. This means
axis=0. What do others think?

Actually, the above would not work in the present implementation if
b.shape=(4,), but one would have to write concatenate((a,b[NewAxis,:])).
Should it be so or should the new axis be prepended automatically? Along
the same lines, shouldn't axes with a single element be "broadcast" as for
addition? 

Carlos



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