@Cache_this(limit=<NUM_LIT:3>, ignore_args=())<EOL><INDENT>def Kdiag(self, X):<DEDENT>
X_prod = self._comp_prod(X)<EOL>return self.variance*four_over_tau*np.arcsin(X_prod/(X_prod+<NUM_LIT:1.>))<EOL>
Compute the diagonal of the covariance matrix for X.