Return a diagonal matrix with vector v on diagonal k. The second argument is optional. If it is positive, the vector is placed on the k-th super-diagonal. If it is negative, it is placed on the -k-th sub-diagonal. The default value of k is 0, and the vector is placed on the main diagonal. For example,
diag ([1, 2, 3], 1) 0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0Given a matrix argument, instead of a vector,
diag
extracts the k-th diagonal of the matrix.