Re: [Outer [Times, , ] ] Question

• To: mathgroup at smc.vnet.net
• Subject: [mg45827] Re: [mg45790] [Outer [Times, , ] ] Question
• From: Yasvir Tesiram <tesiramy at omrf.ouhsc.edu>
• Date: Mon, 26 Jan 2004 01:53:40 -0500 (EST)
• References: <200401250804.DAA19360@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,
There was a discussion on MatrixForm and evaluation recently. And here is
an example where it is simply inconvenient. See those threads in the
archive for a better explanation and ways to evaluate with MatrixForm
display throghout.
A rule I follow is, use MatrixForm only when you want to visualize the
matrix in a Textbook form. It's not really necessary for calculations.
Get rid of the MatrixForm in m1, m2 and m3. Do the calculations for mm and
then display the result in MatrixForm.

I get

In[15]:= mm=m1+m2+m3

Out[15]= {{-1, 1, -1, 1}, {-1, -3, 3, 1}, {-1, 1, -1, 1}, {3, 1, -1, -3},

>    {-1, 1, -1, 1}}

In[16]:= MatrixForm[mm]

Out[16]//MatrixForm= -1   1    -1   1

-1   -3   3    1

-1   1    -1   1

3    1    -1   -3

-1   1    -1   1

Cheers
Yas

On Sun, 25 Jan 2004 MichaelSMcCain at cs.com wrote:

> Hi:
>
> I want to take a Column Vector and multiply it by a Row Vector to create an
> "Outer" Matrix.
>
> In other words, I want to take a 5x1 Column Vector and multiply it by a 1x4
> Row Vector and output a 5x4 Matrix.
>
> I then want to add several of these Matrices together and obtain a "final"
> Matrix.
>
> I tried the following:
>
> x1 = {1, -1, -1, 1, 1};
> y1 = {1, 1, -1, -1};
>
> x2 = {-1, 1, -1, 1, -1};
> y2 = {1, -1, 1, -1};
>
> x3 = {1, 1, -1, -1, 1};
> y3 = {-1, -1, 1, 1};
>
> m1 = MatrixForm[Outer [Times, x1, y1] ]
> m2 = MatrixForm[Outer [Times, x2, y2] ]
> m3 = MatrixForm[Outer [Times, x3, y3] ]
>
> mm = m1 + m2 + m3
>
> MatrixForm[mm]
>
> The output that I get is incorrect and does not combine into a single Matrix.
>
>
> What am I doing wrong?
>
> Thanks,
>
>
> Mike McCain
> MichaelSMcCain at cs.com
>

```

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