[Numpy-discussion] dot product not behaving as expected
Robert Kern
robert.kern@gmail....
Mon Oct 8 11:40:27 CDT 2007
Robin wrote:
> Hi,
>
> I have a problem using numpy.dot, see below:
>
> In [151]: m=5
>
> In [152]: n=5
>
> In [153]: x=(m*ones((1,5)))**arange(0,n)
>
> In [154]: y=test.order_length[::-1]
>
> In [155]: x
> Out[155]: array([[ 1., 5., 25., 125., 625.]])
>
> In [156]: y
> Out[156]:
> array([[ 1024.],
> [ 1280.],
> [ 640.],
> [ 160.],
> [ 20.]])
>
> In [157]: numpy.dot(x,y)
> Out[157]: array([[ 640000.]])
>
> In [158]: sum(x* y.T)
> Out[158]: 55924.0
>
> Am I missing something?
In [1]: from numpy import *
In [2]: x = array([[ 1., 5., 25., 125., 625.]])
In [3]: y = array([[ 1024.],
...: [ 1280.],
...: [ 640.],
...: [ 160.],
...: [ 20.]])
In [4]: dot(x, y)
Out[4]: array([[ 55924.]])
In [5]: sum(x * y.T)
Out[5]: 55924.0
It works for me with a recent SVN numpy on OS X. What version of numpy are you
using? What platform are you on? Did you build with ATLAS or other optimized
linear algebra library?
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
More information about the Numpy-discussion
mailing list