[Numpy-discussion] cross product of two 3xn arrays
Travis Oliphant
oliphant.travis at ieee.org
Fri Feb 17 11:25:59 CST 2006
Charles R Harris wrote:
>On 2/17/06, Bill Baxter <wbaxter at gmail.com> wrote:
>
>
>>For folks using quats to represent rotations (which is all I use them for,
>>anyway), if you're batch transforming a bunch of vectors by one quaternion,
>>it's a lot more efficient to convert the quat to a 3x3 matrix first and
>>transform using matrix multiply (9 mults per transform that way vs 21 or so
>>depending on the implementation of q*v*q^-1). Given that, I can't see many
>>situations when I'd need a super speedy C version of quaternion multiply.
>>
>>--Bill
>>
>>
>
>On a related note, indexing in numarray is some 3x faster than in
>NumPy and I'm wondering what needs to be done to speed that up.
>
>
Please explain with a benchmark. This is not true for all indexing
operations. But, it is possible that certain use cases are faster.
We can't do anything without knowing what you are talking about exactly.
-Travis
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