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MathGroup Archive 1999

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Re: Don't want to calculate scalar product

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19734] Re: [mg19708] Don't want to calculate scalar product
  • From: BobHanlon at aol.com
  • Date: Mon, 13 Sep 1999 02:41:02 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Toshi,

a = {a1, a2, a3}; b = {b1, b2, b3};

a.b

a1 b1 + a2 b2 + a3 b3

Transpose[{a}].{b}

{{a1 b1, a1 b2, a1 b3}, {a2 b1, a2 b2, a2 b3}, {a3 b1, a3 b2, a3 b3}}

a = {1, 2, 3}; b = {4, 5, 6};

a.b

32

Transpose[{a}].{b}

{{4, 5, 6}, {8, 10, 12}, {12, 15, 18}}

Bob Hanlon

In a message dated 9/11/1999 8:36:59 PM, meshii at mech.fukui-u.ac.jp writes:

>I understand that one of the unique point of Mathematica is that you don't
>have to be conscious about whether a vector is a "row" or a "column" vector.
>
>However, I think there is a case in which you have to specify whether you
>want Mathematica to recognize a vector as a row vector or a column vector.
>Let me explain my case.
>
>a={1,2,3}; b={4,5,6}
>
>I want to define "a" as a column vector (3x1 matrix) and "b" as a row vector
>(1x3 matrix).
>
>I expect the product
> a.b
>as a 3x3 matrix, but the answer Mathematica gives is a scalar product "32".
>
>Please give me an advice to get the 3x3 matrix as a product.
>


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