# [Haskell-cafe] multMM :: Matrix -> Matrix -> Matrix --multiplies two matrices question (Homework)

Hans Aberg haberg at math.su.se
Wed Feb 3 04:30:06 EST 2010

```On 3 Feb 2010, at 07:38, 조광래 wrote:

> hi i was trying to solve it but
>
> All i got is
> type Matrix=[[Double]]
>
> multMM :: Matrix -> Matrix -> Matrix --multiplies two matrices
> multMM m t =    [[sum (zipWith (*) (head m)(a)) ] ]where  a = [head
> a | a<-  t]
>
>
> Main> multMM [[2,1,-6],[1,-3,2]] [[1,0,-3],[0,4,20],[-2,1,1]]
> [[14.0]]
>
> from this i could get only the first multiplication 14    that is
> by  2*1 + 1*0 + -6*-2 = 14
>
> how can i make this go throw all rows and colums to get multiple of
> matrixs?

Perhaps you might try the beginners mailing list:
because here, people will just assume one wants effective solutions. :-)

Anyway, the page I mentioned before has a matrix multiplication:
It uses the function transpose(), which is in the module Data.List.

I find looking into the modules of Hugs useful, on my computer they
are in
/usr/local/lib/hugs/packages
but those for GHC are also available online: