[Scipy-tickets] [SciPy] #675: Hadamard function
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Wed Mar 24 08:37:21 CDT 2010
#675: Hadamard function
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Reporter: Ivo | Owner: somebody
Type: enhancement | Status: needs_review
Priority: normal | Milestone: 0.8.0
Component: scipy.linalg | Version:
Keywords: |
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Comment(by warren):
Replying to [comment:4 charris]:
> Why not use the numpy log2 function? Or one of the other methods of
checking for a power of two? For example, n == (-n & n) works for positive
two's complement integers.
>
For a base-2 log of a scalar, my preference is math.log. It is faster
than numpy's log2. I realize speed is not crucial when it is used just
once at the beginning of a function--I guess that's just the way I paint
my bikeshed. :) Is there a compelling reason to *not* use math.log?
As long as it is first verified that n is an int, `n == (-n & n)` would
also work. But the function needs the base-2 log for the loop anyway, so
I don't think much is gained by that--unless the loop were rewritten using
something like `while n:` with `n >>= 1` in the loop. That could work,
but I see that as just different, not necessarily better.
> Are you going to include a fast Hadamard transform also? It is simpler
than the Walsh transform and you can get from one to the other by indexing
with a Grey code.
That sounds like a great idea, but I am not planning to add this.
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Ticket URL: <http://projects.scipy.org/scipy/ticket/675#comment:5>
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