Writes the options in YAML format to a file.

        :param str filename: Target file to write the options.

def write_options_to_YAML(self, filename):
        """Writes the options in YAML format to a file.

        :param str filename: Target file to write the options.
        """
        fd = open(filename, "w")
        yaml.dump(_options_to_dict(self.gc), fd, default_flow_style=False)
        fd.close()