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RE: 3D array

From: John W. Eaton
Subject: RE: 3D array
Date: Tue, 13 Nov 2001 19:28:58 -0600

On 13-Nov-2001, address@hidden <address@hidden> wrote:

| Out of interest, how should arithmetic on N dim arrays
| be defined?

I'm no expert, but element-by-element operations seem straightforward
to me.  I suppose there are other things that make sense for tensors.
At least a generalized inner product, which Matlab seems to have under
the name times, but not for the operator *.  Odd.

As for things like

  svd (some_Nd_matrix);

your guess is as good as mine (and why I would vote for leaving it
undefined in Octave).

| I haven't used N dim arrays in Matlab. For those who have:
| Is that Matlab implementation well thought out?
| Or are there inconsistencies and ambiguities (as is
| fairly common in some of the worse thought out parts of
| Matlab syntax)?

Well, it is apparently impossible to enter an N-d matrix directly
using the "[...]" syntax because of the historical interpretation of
things like

  [[1, 2; 3, 4], [5, 6; 7 8]]

(In Mathematica, I think you would use

  {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}}

though I tend to become confused about what is a row and what is a


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