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Re: Working with arrays

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131210] Re: Working with arrays
  • From: "Kevin J. McCann" <kjm at KevinMcCann.com>
  • Date: Mon, 17 Jun 2013 06:29:32 -0400 (EDT)
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Use a period instead of a CenterDot, as you did in the "Second case".

Cheers,
Kevin

On 6/16/2013 5:12 AM, amannucci wrote:
> I thought I understood variables. This sequence completely mystifies me:
> Clear[lA, xtest]
> lA = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
> xtest = {4, 5, 6};
> lA\[CenterDot]xtest (* First case *)
> {{a, b}, {c, d}} . {x, y} (* Second case *)
>
> The output is:
>
> {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}\[CenterDot]{4, 5, 6}
>
> {a x + b y, c x + d y}
>
> How do I force matrix multiplication to actually occur, as in the second answer? Why does Mathematica do the matrix multiply in the second case but not the first?
>
> Thanks for any help.
>
> -Tony
>



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