def K(self):
        """Kernel matrix

        Returns
        -------
        K : array-like, shape=[n_samples, n_samples]
            kernel matrix defined as the adjacency matrix with
            ones down the diagonal
        """
        try:
            return self._kernel
        except AttributeError:
            self._kernel = self._build_kernel()
            return self._kernel
Kernel matrix

        Returns
        -------
        K : array-like, shape=[n_samples, n_samples]
            kernel matrix defined as the adjacency matrix with
            ones down the diagonal