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Re^2: Perl PDL slower than python numpy

by sgt (Deacon)
on Sep 22, 2020 at 15:09 UTC ( #11122088=note: print w/replies, xml ) Need Help??

in reply to Re: Perl PDL slower than python numpy (Updated2)
in thread Perl PDL slower than python numpy

As quick googling shows, default data type for numpy is 32-bit "single precision" "float"

Are you really sure? I was surprised by your claim that numpy use a default C float. I am a longtime Perl and C hacker and no python expert. But I view the C float type as kind of archaic I use many math libs and the trend is to go past the C double. It would be surprising for a modern lib like numpy to use such a default. Also float() in python means floating point not C float.

Note that I do not really care if tool X is faster that tool Y when the sun, jupiter and the moon are aligned. But I did a bit of web search and could not _quickly_ come up with a definite answer! so I decided to check. Seems that numpy default is a C double:

% steph@kerangi (/tmp/cpanm_t.d) % % python3.8 -c 'import math as m; print(m.sin(float(1)))' 0.8414709848078965 % steph@kerangi (/tmp/cpanm_t.d) % % python3.7 Python 3.7.7 (default, Apr 10 2020, 07:59:19) [GCC 9.3.0] on cygwin Type "help", "copyright", "credits" or "license" for more information. >>> import numpy as np >>> np.float <class 'float'> >>> np.float64 <class 'numpy.float64'> >>> np.float32 <class 'numpy.float32'> >>> print(np.sin(float(1))) 0.8414709848078965 >>> print(np.sin(np.float64(1))) 0.8414709848078965 >>> print(np.sin(np.float32(1))) 0.84147096 >>>

I think that PDL is really a fantastic piece of software and that it is pretty fast. One possible pitfall, common to all C extensions to Perl, is to go back and forth too many times between Perl and C as that can make a computation much slower. It is often possible to avoid it.

hth cheers --sgt

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