private void paintNodes(Graphics2D g) {
		for (Node node : model.getNodes()) {
			Color color = node.getColor();
			double diameter = min_size*node.getDiameter();
			// we draw the circle:
			g.setColor(color);
			g.fillOval((int)(margin_x+node.pos_x*min_size-diameter/2), 
			           (int)(margin_y+node.pos_y*min_size-diameter/2), 
			           (int)diameter, (int)diameter);
			// we draw the text (node number / ...)
			g.setColor(Color.BLACK);
			g.drawString(Integer.toString(node.getNodeNumber()),
			             (int)(margin_x+node.pos_x*min_size -7),
			             (int)(margin_y+node.pos_y*min_size +4));
		}

	}