[Numpy-discussion] Initialization of array?
Rob W. W. Hooft
rob at hooft.net
Thu Nov 30 09:33:46 CST 2000
KH> I had another look at the definition of "ones" and of another routine
KH> I frequently use: arange. It appears that even without rewriting them
KH> in C, some speedup can be achieved:
KH>
KH> - in ones(), the + 1 should be done "in place", saving about 15%, more
KH> if you run out of processor cache:
KH> I'd also try assignment in place:
KH> def ones(shape, typecode='l', savespace=0):
KH> a = zeros(shape, typecode, savespace)
KH> a[len(shape)*[slice(0, None)]] = 1
KH> return a
This is even faster, but it is better to write "a[...] = 1", because
your manual calculation of "..." gives a large overhead for small arrays.
On another machine this time:
Numeric.ones 10 -> 0.254ms
Numeric.ones 100 -> 0.268ms
Numeric.ones 1000 -> 0.340ms
Numeric.ones 10000 -> 1.960ms
Numeric.ones 100000 -> 29.300ms
Numeric.zeros 10 -> 0.055ms
Numeric.zeros 100 -> 0.059ms
Numeric.zeros 1000 -> 0.068ms
Numeric.zeros 10000 -> 0.430ms
Numeric.zeros 100000 -> 9.800ms
Add inplace 10 -> 0.246ms
Add inplace 100 -> 0.255ms
Add inplace 1000 -> 0.312ms
Add inplace 10000 -> 1.270ms
Add inplace 100000 -> 18.100ms
Assign inplace 10 -> 0.192ms
Assign inplace 100 -> 0.201ms
Assign inplace 1000 -> 0.242ms
Assign inplace 10000 -> 1.010ms
Assign inplace 100000 -> 16.300ms
Reshape 1 10 -> 0.842ms
Reshape 1 100 -> 1.175ms
Reshape 1 1000 -> 4.100ms
Reshape 1 10000 -> 35.100ms
Reshape 1 100000 -> 368.600ms
Rob
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