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function C = diag (A, k)
%DIAG diagonal matrices and diagonals of a matrix.
% C = diag (v,k) when v is a vector with n components is a square sparse
% matrix of dimension n+abs(k), with the elements of v on the kth
% diagonal. The main diagonal is k = 0; k > 0 is above the diagonal, and
% k < 0 is below the main diagonal. C = diag (v) is the same as
% C = diag (v,0).
%
% c = diag (A,k) when A is a matrix returns a column vector c formed the
% entries on the kth diagonal of A. The main diagonal is c = diag (A).
%
% The GraphBLAS diag function always constructs a GraphBLAS sparse
% matrix, unlike the built-in diag, which always constructs a full
% matrix. To use this overloaded function for a non-@GrB sparse matrix
% A, use C = diag (A, GrB (k)) ;
%
% Examples:
%
% C1 = diag (GrB (1:10, 'uint8'), 2)
% C2 = sparse (diag (1:10, 2))
% nothing = double (C1-C2)
%
% A = magic (8)
% full (double ([diag(A,1) diag(GrB(A),1)]))
%
% m = 5 ;
% f = ones (2*m,1) ;
% A = diag(-m:m) + diag(f,1) + diag(f,-1)
% G = diag(GrB(-m:m)) + diag(GrB(f),1) + diag(GrB(f),-1)
% nothing = double (A-G)
%
% See also GrB/diag, spdiags, GrB/tril, GrB/triu, GrB.select.
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
% SPDX-License-Identifier: Apache-2.0
if (isobject (A))
A = A.opaque ;
end
if (nargin < 2)
k = 0 ;
else
k = gb_get_scalar (k) ;
end
[am, an, ~] = gbsize (A) ;
a_is_vector = (am == 1) || (an == 1) ;
if (a_is_vector)
% ensure A is a column vector
if (am == 1)
A = gbtrans (A) ;
end
% C = diag (v,k) where v is a column vector and C is a matrix
C = GrB (gbmdiag (A, k)) ;
else
% v = diag (A,k) is a column vector formed from the elements of the kth
% diagonal of A
C = GrB (gbvdiag (A, k)) ;
end
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