matrix multiplication (newbie question)

Sven Schreiber svetosch at gmx.net
Wed Nov 8 08:51:09 CST 2006


izak marais schrieb:
> Hi
> 
> Sorry if this is an obvious question, but what is the easiest way to
> multiply matrices in numpy? Suppose I want to do A=B*C*D. The ' * '
> operator apparently does element wise multiplication, as does the
> 'multiply' ufunc. All I could find was the numeric function
> 'matrix_multiply, but this only takes two arguments.
> 
> Thanks in advance!
> Izak

There are (at least) two ways:

You can use 'dot', possibly nested.

or you can convert your arrays into the matrix subclass, for which '*'
is matrix multiplication. I.e. mat(B)*mat(C)*mat(D) does what you want.

If you "only" deal with algebra-style matrices (2d-arrays), consider
using the matrix subclass as much as you can. E.g. use the functions in
numpy.matlib to build your inputs.
-sven

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