description: B = tril(A,k) extracts lower triangular part of A. tril(A) is the lower triangular part of A. tril(A,k) is the elements on and below the k-th diagonal of A. k = 0 is the main diagonal, k > 0 is above the main diagonal and k < 0 is below the main diagonal. arguments: A is a matrix of NCpolys k is an integer output: matrix of NCpolys possible usage: tril(A), tril(A,k) example: >> A=[x x^2 x*y-y*x; y x*y 2*x-y; x+y y-x x^2+y^2] A = x x^2 x*y-y*x y x*y 2*x-y x+y -x+y x^2+y^2 >> tril(A) ans = x 0 0 y x*y 0 x+y -x+y x^2+y^2 >> tril(A,-1) ans = 0 0 0 y 0 0 x+y -x+y 0 |