function writeGraph(nodes, edges, fileName)
%WRITEGRAPH Write a graph to an ascii file
%
%   writeGraph(NODES, EDGES, FILENAME)
%
%   Example
%     % create a basic graph and save it to a file
%     nodes = [10 10;20 10;10 20;20 20;27 15];
%     edges = [1 2;1 3;2 4;2 5;3 4;4 5];
%     writeGraph(nodes, edges, 'simpleGraph.txt');
%
%   See also
%     readGraph
%
% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2014-01-20,    using Matlab 7.9.0.529 (R2009b)
% Copyright 2014 INRA - Cepia Software Platform.


%% File creation and init

% extract "sizes" of the graph
nNodes = size(nodes, 1);
nEdges = size(edges, 1);
nDims  = size(nodes, 2);

% file opening
f = fopen(fileName, 'wt');
if f == -1
    error(['could not open file for writing: ' fileName]);
end

% write header
fprintf(f, '# graph\n');


%% write nodes info

fprintf(f, '# nodes\n');
fprintf(f, '%d %d\n', nNodes, nDims);
format = ['%g' repmat(' %g', 1, nDims-1) '\n'];
for iNode = 1:nNodes
    fprintf(f, format, nodes(iNode, :));
end

%% write edges info

fprintf(f, '# edges\n');
fprintf(f, '%d\n', nEdges);

format = '%d %d\n';
for iEdge = 1:nEdges
    fprintf(f, format, edges(iEdge, :));
end

% close file
fclose(f);
