% -*- texinfo -*-
% @deftypefn {Function File} {[@var{c}, @var{lev}] =} contourc (@var{x}, @var{y}, @var{z}, @var{vn})
% Compute isolines (contour lines) of the matrix @var{z}.
% Parameters @var{x}, @var{y} and @var{vn} are optional.
%
% The return value @var{lev} is a vector of the contour levels.
% The return value @var{c} is a 2 by @var{n} matrix containing the
% contour lines in the following format
%
% @example
% @group
% @var{c} = [lev1, x1, x2, @dots{}, levn, x1, x2, @dots{}
% len1, y1, y2, @dots{}, lenn, y1, y2, @dots{}]
% @end group
% @end example
%
% @noindent
% in which contour line @var{n} has a level (height) of @var{levn} and
% length of @var{lenn}.
%
% If @var{x} and @var{y} are omitted they are taken as the row/column
% index of @var{z}. @var{vn} is either a scalar denoting the number of lines
% to compute or a vector containing the values of the lines. If only one
% value is wanted, set @code{@var{vn} = [val, val]};
% If @var{vn} is omitted it defaults to 10.
%
% For example,
% @example
% @group
% x = 0:2;
% y = x;
% z = x' * y;
% contourc (x, y, z, 2:3)
% @result{} 2.0000 2.0000 1.0000 3.0000 1.5000 2.0000
% 2.0000 1.0000 2.0000 2.0000 2.0000 1.5000
%
% @end group
% @end example
% @seealso{contour}
% @end deftypefn