Re: Row or column?

• To: mathgroup at smc.vnet.net
• Subject: [mg112708] Re: Row or column?
• From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
• Date: Tue, 28 Sep 2010 06:02:31 -0400 (EDT)
• References: <i7mq4c\$ovt\$1@smc.vnet.net> <i7pp9j\$leh\$1@smc.vnet.net>

```This lack of distinction between rows and columns can be a problem.
Consider:

a.Transpose[a]     and     Transpose[a].a

Kevin

On 9/27/2010 5:48 AM, Sjoerd C. de Vries wrote:
> Sam,
>
> Mathematica considers the first level of a list as rows, the second,
> nested, levels are the columns etc. So, for display purposes {{a, b}}
> would show as a row, but if you want to use it for matrix/vector
> multiplication you only need {a,b}, as Mathematica does not
> differentiate between row or column vectors.
>
> Cheers -- Sjoerd
>
> On Sep 26, 8:44 am, Sam Takoy<sam.ta... at yahoo.com>  wrote:
>> Hi,
>>
>> How come
>>
>> {a, b} // MatrixForm
>> {{a}, { b}} // MatrixForm
>>
>> produce identical outputs: columns?
>>
>> I would think that the first "matrix" is 1x2 and the second is 2x1.
>>
>> Alternatively, how do I produce a 1x2 matrix?
>>