// You can pass aditional parameters as pairs. 
// Example graph_to_dot(adj, 'filename', 'myfile.txt')
// 'filename' - string (default is 'tmp.dot')
// 'node_label' - array of strings (node labels)
function write_mat_to_file(adj, varargin)
  
  // Parameters
  directed = 1
  filename = 'tmp.dot';
  arc_label = [];
  node_label = [];
  width = 10; 
  height = 10;
  
  // Read user parameters
  nargin = length(varargin)
  for i = 1:2:nargin-1
    if varargin(i) == 'node_label' then
      node_label = varargin(i+1);
    elseif varargin(i) == 'arc_label' then
      arc_label = varargin(i+1);
    end    
  end
  
  handler = mopen(filename, 'w');  
  
  // Check for errors
  if (handler == -1)  then
    error('Cannot open file for writing')
  end
  
  if  directed then
    mfprintf(handler, 'digraph G{\n');
    arctxt = '->';
    if isempty(arc_label)
      labeltxt = '';
    end
  else
    mfprintf(handler, 'graph G{\n');
    arctxt = '--';               
  end
  
  mfprintf(handler, 'center = 1;\n');
  
  // Node data
  dims = size(adj);
  nnodes = dims(1);
  
  disp('nnodes: ');
  disp(nnodes);
  for node =1:nnodes
    if isempty(node_label) then
      mfprintf(handler, '%d;\n', node);
    else
      mfprintf(handler, '%d [label = %s];\n', node, node_label(node));            
    end
  end
  
  // Edge data
  for node1=1:nnodes
    for node2=1:nnodes
      
      val = adj(node1, node2)
      
      if (val == 1) then
        
        mfprintf(handler, '%d ' + arctxt + ' %d', node1, node2);
        
        if (~isempty(arc_label)) then
          mfprintf(handler, ' [label = %s];', arc_label(node1, node2));
        end
        
        mfprintf(handler, '\n');        
      end
      
    end
  end
  
  mfprintf(handler, '}\n');
  
  mclose(handler);
  
endfunction

node_labels = ['A', 'B', 'C'];
edge_labels = ['','10',''; '','','12'; '15','',''];
mat = [0,1,0 ; 0,0,1; 1,0,0];
write_mat_to_file(mat, 'node_label', node_labels, 'arc_label', edge_labels);