Print the matrix for self's nodes.

        Args:
            format (str): output format (csv, json or text).
            output (file): file descriptor on which to write.
            depth (int): depth of the matrix.

def print_matrix(self, format=None, output=sys.stdout, depth=0, **kwargs):
        """
        Print the matrix for self's nodes.

        Args:
            format (str): output format (csv, json or text).
            output (file): file descriptor on which to write.
            depth (int): depth of the matrix.
        """
        matrix = self.as_matrix(depth=depth)
        matrix.print(format=format, output=output, **kwargs)