[Numpy-discussion] Is sum() slow?
Mads Ipsen
mpi at osc.kiku.dk
Mon Mar 6 23:16:02 CST 2006
Hi,
Sorry if this is a double post - unsure if it made it the first time:
Here are some timings that puzzle me a bit. Sum the two rows of a 2xn
matrix, where n is some large number
python -m timeit -s "from numpy import array,sum,reshape; x =
array([1.5]*1000); x = reshape(x,(2,500))" "x.sum(0)"
10000 loops, best of 3: 36.2 usec per loop
python -m timeit -s "from numpy import array,sum,reshape; x =
array([1.5]*1000); x = reshape(x,(2,500))" "x[0] + x[1]"
100000 loops, best of 3: 5.35 usec per loop
The two calculations are completely equivalent (at least from the
numerical results point of view). But using the built-in sum() function is
app. 6 times slower.
Just for the reference - using Numeric gives
python -m timeit -s "from Numeric import array,sum,reshape; x =
array([1.5]*1000); x = reshape(x,(2,500))" "sum(x)"
100000 loops, best of 3: 7.08 usec per loop
Any suggestions to why this might be - or am I doing something wrong here?
Thanks // Mads
PS. Thanks to everybody that responded to my previous posting on problems
and questions regarding rint() and related coding issues. Your replies
were very helpful!
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