def test_train(self):
        poly = Polynomial2D(order=2)
        for x in range(-8,9):
            for y in range(-8,9):
                val = -5 + 3*y + 4*y*y + 2*y*x+ x*x - 2*x
                poly.addTraining(val,[x,y])
        poly.train()
        for x in range(-8,9):
            for y in range(-8,9):
                val  = -5 + 3*y + 2*x - 4*y*y + 2*y*x+ x*x
                pred = poly.predict([x,y])
                self.assertAlmostEqual(val,pred,delta=0.0001)
dataset/ETHPy150Open bolme/pyvision/src/pyvision/vector/Polynomial.py/_PolyTest.test_train/swapped operands of `-`