[Numpy-discussion] dot documentation

T J tjhnson@gmail....
Fri Aug 7 16:19:16 CDT 2009

Hi,  the documentation for dot says that a value error is raised if:

    If the last dimension of a is not the same size as the
second-to-last dimension of b.


This doesn't appear to be the case:

>>> a = array([[1,2],[3,4]])
>>> b = array([1,2])
>>> dot(a,b)

I can see *how* 5,11 is obtained, but it seems this should have raised
a ValueError since the 2 != 1.  So the actual code must do something
more involved.  When I think about broadcasting, it seems that maybe b
should have been broadcasted to:

-->  array([[1,2],[1,2]])

and then the multiplication done as normal (but this would give a 2x2 result).

Can someone explain this to me?

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