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MathGroup Archive 2007

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Re: Matrix Inverse Issue

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80623] Re: Matrix Inverse Issue
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Sun, 26 Aug 2007 23:22:59 -0400 (EDT)

On 8/26/07 at 3:00 AM, brg at nowhere.org (Brian Gladman) 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}]

>A Inverse[A]

>I expected the identity matrix here but I get extra terms.

>Am I doing something wrong?

Yes.

A Inverse[A]

does an element by element multiplication. You want

A.Inverse[A]

which does a matrix multiplication and gives the expected result
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