% -*- texinfo -*-
% @deftypefn {Function File} {} tril (@var{a}, @var{k})
% @deftypefnx {Function File} {} triu (@var{a}, @var{k})
% Return a new matrix formed by extracting the lower (@code{tril})
% or upper (@code{triu}) triangular part of the matrix @var{a}, and
% setting all other elements to zero. The second argument is optional,
% and specifies how many diagonals above or below the main diagonal should
% also be set to zero.
%
% The default value of @var{k} is zero, so that @code{triu} and
% @code{tril} normally include the main diagonal as part of the result
% matrix.
%
% If the value of @var{k} is negative, additional elements above (for
% @code{tril}) or below (for @code{triu}) the main diagonal are also
% selected.
%
% The absolute value of @var{k} must not be greater than the number of
% sub- or super-diagonals.
%
% For example,
%
% @example
% @group
% tril (ones (3), -1)
% @result{} 0 0 0
% 1 0 0
% 1 1 0
% @end group
% @end example
%
% @noindent
% and
%
% @example
% @group
% tril (ones (3), 1)
% @result{} 1 1 0
% 1 1 1
% 1 1 1
% @end group
% @end example
% @seealso{triu, diag}
% @end deftypefn