########################################################################
##
## Copyright (C) 2005-2023 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################

## -*- texinfo -*-
## @deftypefn  {} {} gplot (@var{A}, @var{xy})
## @deftypefnx {} {} gplot (@var{A}, @var{xy}, @var{line_style})
## @deftypefnx {} {[@var{x}, @var{y}] =} gplot (@var{A}, @var{xy})
## Plot a graph defined by @var{A} and @var{xy} in the graph theory sense.
##
## @var{A} is the adjacency matrix of the array to be plotted and @var{xy} is
## an @var{n}-by-2 matrix containing the coordinates of the nodes of the graph.
##
## The optional parameter @var{line_style} defines the output style for the
## plot.  Called with no output arguments the graph is plotted directly.
## Otherwise, return the coordinates of the plot in @var{x} and @var{y}.
## @seealso{treeplot, etreeplot, spy}
## @end deftypefn

function [x, y] = gplot (A, xy, line_style)

  if (nargin < 2)
    print_usage ();
  endif

  if (nargin == 2)
    line_style = "-";
  endif

  [i, j] = find (A);
  xcoord = [xy(i,1), xy(j,1), NaN(length(i),1) ]'(:);
  ycoord = [xy(i,2), xy(j,2), NaN(length(i),1) ]'(:);

  if (nargout == 0)
    plot (xcoord, ycoord, line_style);
  else
    x = xcoord;
    y = ycoord;
  endif

endfunction


%!demo
%! ## Binary Tree Representation
%! A = [0 1 0 0 0 0 0
%!      1 0 1 1 0 0 0
%!      0 1 0 0 0 0 0
%!      0 1 0 0 1 0 0
%!      0 0 0 1 0 1 1
%!      0 0 0 0 1 0 0
%!      0 0 0 0 1 0 0];
%!
%! xy = [1  , 0
%!       1.5, 1
%!       2  , 0
%!       2.5, 2
%!       3.5, 1
%!       3  , 0
%!       4  , 0];
%!
%! clf;
%! gplot (A, xy, "o-");
%! set (get (gca, ("children")), "markersize", 12);
%! title ("gplot() of Binary Tree Adjacency matrix");

## Mark graphical function as tested by demo block
%!assert (1)
