Re: check if a square matrix is diagonal
- To: mathgroup at smc.vnet.net
- Subject: [mg115332] Re: check if a square matrix is diagonal
- From: Sseziwa Mukasa <mukasa at jeol.com>
- Date: Fri, 7 Jan 2011 04:14:09 -0500 (EST)
On Jan 6, 2011, at 2:06 AM, 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
If[mtemp == Table[Table[0, {i, 1, d[[1]]}], {i, 1, d[[2]]}],
True,
False]
Better yet, why not just check that all the off diagonal entries are 0?
checkIfDiagonalMatrix[m_] == Block[{},Do[If[m[[i,j]]!==0,Return[False]],{i,Length[m]},{j,Length[m[[1]]]}];True]
Regards,
Ssezi