[Numpy-discussion] cumsum much slower than simple loop?

Dave Cook daverz@gmail....
Thu Feb 9 23:41:19 CST 2012


On Thu, Feb 9, 2012 at 9:21 PM, <josef.pktd@gmail.com> wrote:

> strange (if I didn't make a mistake)
>
> In [12]: timeit a.cumsum(0)
> 100 loops, best of 3: 7.17 ms per loop
>
> In [13]: timeit a.T.cumsum(-1).T
> 1000 loops, best of 3: 1.78 ms per loop
>
> In [14]: (a.T.cumsum(-1).T == a.cumsum(0)).all()
> Out[14]: True
>
>
Interesting.  I should have mentioned that I'm using numpy 1.5.1 on 64-bit
Ubuntu 10.10.  This transpose/compute/transpose trick did not work for me.

In [27]: timeit a.T.cumsum(-1).T
10 loops, best of 3: 18.3 ms per loop

Dave Cook
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