def gradients_X(self, dL_dK, X, X2=None):
if use_stationary_cython:<EOL><INDENT>return self._gradients_X_cython(dL_dK, X, X2)<EOL><DEDENT>else:<EOL><INDENT>return self._gradients_X_pure(dL_dK, X, X2)<EOL><DEDENT>
Given the derivative of the objective wrt K (dL_dK), compute the derivative wrt X