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Re: How to do symbolic matrix manipulations

• To: mathgroup at smc.vnet.net
• Subject: [mg92304] Re: How to do symbolic matrix manipulations
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Sat, 27 Sep 2008 06:49:48 -0400 (EDT)
• References: <gbjmam$3ab$1@smc.vnet.net>

Peng Yu schrieb:
> Hi,
>
> Suppose I have matrices a and b, which does not have any value yet.
>
> If I write b * a, mathematica would give me "a b". I'm wondering how to make
> it know that a and b are matrices, so that it would give me "b a" rather
> than "a b".
>
> Thanks,
> Peng
>

a*b gives the matrix (a_ij * b_ij) which is the same as (b_ij*a_ij),
so a*b=b*a.

I think you want to do matrix multiplication, which ist done by a.b
or Dot[a,b]. If you enter b.a the result will be b.a not a.b

Gruss Peter
-- 
==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de