Dot product?

[Berthold Höllmann]

"David C. Ullrich" <ullrich at math.okstate.edu> writes:

>     Ok, so I'm dense. How do I take the traditional "dot product"
> of two vectors? In a nice Pythonic sort of way, I mean. Say
> the vectors are represented as sequences of numerics - then
> of course I can say just
> 
> def Dot(X, Y):
>     res = 0
>     for j in range(len(X)):
>         res = res + X[j] * Y[j]
>     return res
> 
> and that gives the right answer, but it doesn't look right -
> seems like the Python way would involve a "for x in X"
> instead of that "for j in range(len(X))".
> 
>     For example if Transpose returns the transpose of a
> sequence of sequences (ie Transpose(s)[j][k] = s[k][j])
> I can say
> 
> def Dot(X, Y):
>     res = 0
>     for (x,y) in Transpose((X,Y)):
>         res = res + x * y
>     return res
> 

How about:

def Dot(X, Y):
    res = 0.
    for (x,y) in map(None, X, Y):
        res = res + x * y
    return res

> and that looks "right". For that matter once I have a
> Transpose I could just use reduce. But when I write
> a Transpose routine I have the same complaints with
> the way it looks, only more so.
> 
>     Is there a keen way to do this sort of thing, or do I
> just have to use the index as above? (Come to think
> of it I think what I really want is a nice Transpose -
> that's been coming up a lot, Dot is just one place.)
> 
Cheers

Berthold
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