No, I don't have permission to edit.

Nicolas

On 27 May, 2009, at 18:01 , Charles R Harris wrote:

On Wed, May 27, 2009 at 9:31 AM, Nicolas Rougier <Nicolas.Rougier@loria.fr

wrote:

Hi,

I've written a very simple benchmark on recarrays:

import numpy, time

Z = numpy.zeros((100,100), dtype=numpy.float64) Z_fast = numpy.zeros((100,100), dtype=[('x',numpy.float64), ('y',numpy.int32)]) Z_slow = numpy.zeros((100,100), dtype=[('x',numpy.float64), ('y',numpy.bool)])

t = time.clock() for i in range(10000): Z*Z print time.clock()-t

t = time.clock() for i in range(10000): Z_fast['x']*Z_fast['x'] print time.clock()-t

t = time.clock() for i in range(10000): Z_slow['x']*Z_slow['x'] print time.clock()-t

And got the following results: 0.23 0.37 3.96

Am I right in thinking that the last case is quite slow because of some memory misalignment between float64 and bool or is there some machinery behind that makes things slow in this case ?

Probably. Record arrays are stored like packed c structures and need to be unpacked by copying the bytes to aligned data types.

Should this be mentioned somewhere in the recarray documentation ?

A note would be appropriate, yes. You should be able to do that, do you have edit permissions for the documentation?

Chuck

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