Newbie question about numpy

[Avell Diroll]

Paul Johnston wrote:
(snip)
> I noted the lack of matrices so installed numpy
(snip)
> _________________________________________________________
> from numpy  import *
> 
> a = array([[1,2,3],[4,5,6],[1,2,3]])
> b = array([[1,3,6],[2,5,1],[1,1,1]])
(snip)
> print "a * b is \n", a * b
> _________________________________________________________
(snip)
> a * b is
> [[ 1  6 18]
>  [ 8 25  6]
>  [ 1  2  3]]
> _________________________________________________________
> 
> 
> I know its a long time since my degree but that's not matrix
> multiplication is it ?

You consider that a and b are matrices, but for the python interpreter
they are arrays so a*b returns the multiplication of 2 arrays.

For matrices multiplication, you could get a hint by typing the
following in the interpreter :

>>> import numpy
>>> dir(numpy)
>>> help(numpy.matrixmultiply)    #type "q" to exit

which could make you want to try the following code :

>>> from numpy  import *
>>> a = array([[1,2,3],[4,5,6],[1,2,3]])
>>> b = array([[1,3,6],[2,5,1],[1,1,1]])
>>> print matrixmultiply(a,b)

...
output :
...

array([[ 8, 16, 11],
       [20, 43, 35],
       [ 8, 16, 11]])
...

HIH,
avell