[Numpy-discussion] vector cross product

[David M. Cooke]

"Gary Ruben" <gazzar at email.com> writes:

> I guess from the lack of enthusiastic responses that there aren't
> many out there who think this is of interest. So, perhaps Todd could
> just add it to the bottom of the list of possible ideas I imagine he
> maintains, so that if it comes up again in the future, it is at
> least noted. thanks, Gary

If all you need is a 3-dimensional vector class, I've just whipped
one up using Pyrex. (I needed it for something else.)

It just does 3-vectors, and it's quite similiar to Konrad Hinsen's
Vector class, although the components are referenced by attributes
(using properties) instead of methods.

Get it at
http://arbutus.mcmaster.ca/dmc/software/
It's called the inventive name of vector3.

Here's a speed comparision:

$ timeit.py -s 'from Scientific.Geometry import Vector as V' 'V(1,2,3).angle(V(4,5,6))'
10000 loops, best of 3: 40.5 usec per loop
$ timeit.py -s 'from vector3 import Vector3 as V' 'V(1,2,3).angle(V(4,5,6))'
1000000 loops, best of 3: 1.87 usec per loop

[I'm also working on an n-dimensional vector class using Pyrex, more
along the lines of a 1-dimensional, contiguous, Numeric or numarray
array. Currently, it's 3x and 5.5x times faster, respectively, for
adding 1000-element vectors. I'm not ready to release it yet, though.]

> ----- Original Message -----
> From: "Gary Ruben" <gazzar at email.com>
> To: numpy-discussion at lists.sourceforge.net
> Subject: [Numpy-discussion] vector cross product
> Date: Sun, 31 Oct 2004 22:18:56 +1000
>
>> 
>> Not that I have a really urgent need, but is there a reason that
>> nice, fast C-based vector operations aren't implemented in Numeric
>> or numarray? I notice Fernando Perez has a cross product as a
>> useful SciPy weave example on his site. I've also seen comments
>> elsewhere about Numpy's lack of a cross product. eg.
>> <http://mail.python.org/pipermail/python-list/2004-March/213878.html>
>> I'm using Konrad Hinsen's Scientific Python for the convenience
>> value of his Vector class, which also provides a nice angle()
>> method but it bothers me that it's implemented in native Python.
>> The Vector type in vpython probably does it 'properly', but I don't
>> use it just for the convenience since it adds an extra dependency
>> to my code.
>> 
>> comments?
>> Gary R.

-- 
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|David M. Cooke                      http://arbutus.physics.mcmaster.ca/dmc/
|cookedm at physics.mcmaster.ca