G is upper-triangular, so G.T should be lower-triangular.

Author: kaicheng

sklearn/gaussian_process/gaussian_process.py

@@ -474,7 +474,8 @@ def predict(self, X, eval_MSE=False, batch_size=None):
                 if self.beta0 is None:
                     # Universal Kriging
                     u = linalg.solve_triangular(self.G.T,
-                                                np.dot(self.Ft.T, rt) - f.T)
+                                                np.dot(self.Ft.T, rt) - f.T,
+                                                lower=True)
                 else:
                     # Ordinary Kriging
                     u = np.zeros((n_targets, n_eval))