[Numpy-discussion] matrix default to column vector?

Olivier Verdier zelbier@gmail....
Sun Jun 7 04:44:19 CDT 2009


Yes, I found the thread you are referring to:
http://mail.python.org/pipermail/python-dev/2008-July/081554.html

However, since A*B*C exists for matrices and actually computes (A*B)*C, why
not do the same with dot? I.e. why not decide that dot(A,B,C) does what
would A*B*C do, i.e., dot(dot(A,B),C)?
The performance and precision problems are the responsability of the user,
just as with the formula A*B*C.
== Olivier

2009/6/7 Robert Kern <robert.kern@gmail.com>

> On Sun, Jun 7, 2009 at 02:43, Olivier Verdier <zelbier@gmail.com> wrote:
> > There would be a much simpler solution than allowing a new operator. Just
> > allow the numpy function dot to take more than two arguments. Then A*B*C
> in
> > matrix notation would simply be:
> > dot(A,B,C)
> > with arrays. Wouldn't that make everybody happy? Plus it does not break
> > backward compatibility. Am I missing something?
>
> We've discussed it before. Search the archives. Although matrix
> multiplication is mathematically associative, there are performance
> and precision implications to the order the multiplications happen. No
> satisfactory implementation was found.
>
> --
> Robert Kern
>
> "I have come to believe that the whole world is an enigma, a harmless
> enigma that is made terrible by our own mad attempt to interpret it as
> though it had an underlying truth."
>  -- Umberto Eco
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