24.11 Triangular Matrices

  • DiagonalOfMat( mat ) O

    returns the diagonal of mat as a list. 

    gap> DiagonalOfMat([[1,2],[3,4]]);
[ 1, 4 ]
  • UpperSubdiagonal( mat, pos ) O

    returns a mutable list containing the entries of the posth upper subdiagonal of mat. 

    gap> UpperSubdiagonal(mat,1);
[ 2, 6 ]
  • DepthOfUpperTriangularMatrix( mat ) A

    If mat is an upper triangular matrix this attribute returns the index of the first nonzero diagonal. 

    gap> DepthOfUpperTriangularMatrix([[0,1,2],[0,0,1],[0,0,0]]);
1
gap> DepthOfUpperTriangularMatrix([[0,0,2],[0,0,0],[0,0,0]]);  
2

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    GAP 4 manual
    February 2000