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MathGroup Archive 2007

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Re: [?? Probable Spam] Matrix Inverse Issue

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80620] Re: [?? Probable Spam] [mg80556] Matrix Inverse Issue
  • From: DrMajorBob <drmajorbob at bigfoot.com>
  • Date: Sun, 26 Aug 2007 23:21:25 -0400 (EDT)
  • References: <14064259.1188136825413.JavaMail.root@m35>
  • Reply-to: drmajorbob at bigfoot.com

You mean a.Inverse[a] (vector/matrix Dot product), not a*Inverse[a]  
(term-wise product).

Bobby

On Sun, 26 Aug 2007 02:00:40 -0500, Brian Gladman <brg at nowhere.org> wrote:

> I am having a problem with the matrix inverse for the following matrix in
> Mathematica 6:
>
> A = Table[If[j == i, 1 - i/10, If[j == i + 1, i/10, 0]], {i,9}, {j, 9}]
>
> {{9/10, 1/10, 0, 0, 0, 0, 0, 0, 0}, {0, 4/5, 1/5, 0, 0, 0, 0, 0,
>   0}, {0, 0, 7/10, 3/10, 0, 0, 0, 0, 0}, {0, 0, 0, 3/5, 2/5, 0, 0, 0,
>   0}, {0, 0, 0, 0, 1/2, 1/2, 0, 0, 0}, {0, 0, 0, 0, 0, 2/5, 3/5, 0,
>   0}, {0, 0, 0, 0, 0, 0, 3/10, 7/10, 0}, {0, 0, 0, 0, 0, 0, 0, 1/5, 4/
>   5}, {0, 0, 0, 0, 0, 0, 0, 0, 1/10}}
>
> A Inverse[A]
>
> {{1, -1/72, 0, 0, 0, 0, 0, 0, 0}, {0, 1, -1/14, 0, 0, 0, 0, 0, 0}, {0,
>    0, 1, -3/14, 0, 0, 0, 0, 0}, {0, 0, 0, 1, -8/15, 0, 0, 0, 0}, {0,
>   0, 0, 0, 1, -5/4, 0, 0, 0}, {0, 0, 0, 0, 0, 1, -3, 0, 0}, {0, 0, 0,
>   0, 0, 0, 1, -49/6, 0}, {0, 0, 0, 0, 0, 0, 0, 1, -32}, {0, 0, 0, 0,
>   0, 0, 0, 0, 1}}
>
> I expected the identity matrix here but I get extra terms.
>
> Am I doing something wrong?
>
>    Brian Gladman
>
>
>



-- 

DrMajorBob at bigfoot.com


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