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Re: check if a square matrix is diagonal

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115330] Re: check if a square matrix is diagonal
  • From: Peter Breitfeld <phbrf at t-online.de>
  • Date: Fri, 7 Jan 2011 04:13:47 -0500 (EST)
  • References: <ig3pkm$jh5$1@smc.vnet.net>

benyaya wrote:

> What I try to do is extract the diagonal, subtract if from the matrix,
> then compare the new matrix with 0.
> My code doesn't work out though, can anyone help? thanks a lot.
>
> checkIfDiagonalMatrix[m_] = Module[{d, mtemp},
>   d = Dimensions[m];
>   mtemp = DiagonalMatrix[Diagonal[m]] - m;
>   If[mtemp == Table[Table[0, {i, 1, d}], {i, 1, d}],
>    True,
>    False]
>   ]
>

Try this:

isDiagonalMatrix[m_?MatrixQ] := (DiagonalMatrix@Diagonal[m] == m)

-- 
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de


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