[Numpy-discussion] matrix default to column vector?
Alan G Isaac
aisaac at american.edu
Sun Jun 7 20:12:42 EDT 2009
>> On Sun, Jun 7, 2009 at 04:44, Olivier Verdier <zelbier at gmail.com> wrote:
>>> 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.
> Robert Kern wrote:
>> I'm happy to make the user responsible for performance and precision
>> problems if he has the tools to handle them. The operator gives the
>> user the easy ability to decide the precedence with parentheses. The
>> function does not.
On 6/7/2009 7:44 PM Eric Firing apparently wrote:
> The function could, with suitable parsing of the argument(s):
> (A*B)*C => dot( ((A,B),C) ) or dot( (A,B), C )
> A*(B*C) => dot( (A, (B,C)) ) or dot( A, (B,C) )
> Effectively, the comma is becoming the operator.
Horribly implicit and hard to read!
If something needs to be done to make ``dot``
approach the convenience of ``*``, I think that
adding ``dot`` as an array method looks
attractive.
(A*B)*C => A.dot(B).dot(C)
A*(B*C) => A.dot( B.dot(C) )
But no matter how you slice it, the left
hand expression is more compact and
easier to read.
fwiw,
Alan Isaac
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