def _traverse_grid_(self):
        """ Solve using linear systems of equations """
        P, L, U = linalg.lu(self.coeffs)
        aux = np.zeros(1-self.M)

        for j in reversed(range(self.N)):
            aux[0] = np.dot(-self.a[1], self.grid[0, j])
            x1 = linalg.solve(L, self.grid[1:self.M, j+1]+aux)
            x2 = linalg.solve(U, x1)
            self.grid[1:self.M, j] = x2
dataset/ETHPy150Open jamesmawm/Mastering-Python-for-Finance-source-codes/B03898_04_codes/FDImplicitEu.py/FDImplicitEu._traverse_grid_/swapped operands of `-`