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