[Numpy-discussion] dot product not behaving as expected
Robin
robince@gmail....
Mon Oct 8 11:57:37 CDT 2007
>
> 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?
I am on Ubuntu 7.04, gcc 4.1.2
In [181]: numpy.__version__
Out[181]: '1.0.4.dev4155'
Built with ATLAS 3.7.37, Lapack 3.1.1
It also occurs for me on Windows XP SP2 with 1.0.4dev4154 built with cygwin
gcc 3.4.4 and atlas 3.7.37 and lapack 3.1.1.
Actually I found that for me it also doesn't occur if I type them in like
that. The problem comes when y is reverse with the [::-1] index. Is this the
correct way to reverse a vector?
Anyway try this:
In [36]: x=array([[1.,5.,25.,125.,625.]])
In [37]: y=array([[20.],[160.],[640.],[1280.],[1024.]])
In [38]: y
Out[38]:
array([[ 20.],
[ 160.],
[ 640.],
[ 1280.],
[ 1024.]])
In [39]: y2=y[::-1]
In [40]: y2
Out[40]:
array([[ 1024.],
[ 1280.],
[ 640.],
[ 160.],
[ 20.]])
In [41]: dot(x,y)
Out[41]: array([[ 816820.]])
In [42]: dot(x,y2)
Out[42]: array([[ 640000.]])
Thanks,
Robin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://projects.scipy.org/pipermail/numpy-discussion/attachments/20071008/c6397763/attachment.html
More information about the Numpy-discussion
mailing list