Re: Transpose[A]*A wrong?
- To: mathgroup at smc.vnet.net
- Subject: [mg41193] Re: Transpose[A]*A wrong?
- From: Petr Kujan <kujanp at fel.cvut.cz>
- Date: Tue, 6 May 2003 06:07:56 -0400 (EDT)
- Organization: Czech Technical University
- References: <b950vl$r49$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Daniel Lidström wrote:
>Hi,
>
>why does Mathematica give the wrong result here?
>
>In[1]:= \!\(A\ = \ {{x\_11, x\_12, x\_13}, {x\_21, x\_22, x\_23}, {x\_31,
>x\_32,
> x\_33}}\)
>
>Out[1]= {{x , x , x }, {x , x , x }, {x , x , x }}
> 11 12 13 21 22 23 31 32 33
>
>In[2]:= Transpose[A]*A
>
> 2 2
>2
>Out[2]= {{x , x x , x x }, {x x , x , x x }, {x x , x x
>, x }}
> 11 12 21 13 31 12 21 22 23 32 13 31 23
>32 33
>
>Look at the diagonal elements for example.
>Thanks!
>
>/Daniel
>
>
>
Hi Daniel,
function - Times[ ] .. "*" -> array multiply,
function - Dot[ ] .. "." -> matrix multiply.
Now it's matrix multiply:
In[9]:=
\!\(A\ = \ {{x\_11, x\_12, x\_13}, {x\_21, x\_22, x\_23}, {x\_31, x\_32,
x\_33}}\)
Out[9]=
\!\({{x\_11, x\_12, x\_13}, {x\_21, x\_22, x\_23}, {x\_31, x\_32, x\_33}}\)
In[8]:=
Transpose[A].A
Out[8]=
\!\({{x\_11\%2 + x\_21\%2 + x\_31\%2,
x\_11\ x\_12 + x\_21\ x\_22 + x\_31\ x\_32,
x\_11\ x\_13 + x\_21\ x\_23 + x\_31\ x\_33}, {x\_11\ x\_12 +
x\_21\ x\_22 + x\_31\ x\_32, x\_12\%2 + x\_22\%2 + x\_32\%2,
x\_12\ x\_13 + x\_22\ x\_23 + x\_32\ x\_33}, {x\_11\ x\_13 +
x\_21\ x\_23 + x\_31\ x\_33,
x\_12\ x\_13 + x\_22\ x\_23 + x\_32\ x\_33,
x\_13\%2 + x\_23\%2 + x\_33\%2}}\)
Petr