張量的兩種運算
1. 張量的乘（Tensor product）
tensorproduct()
2. 張量的縮並
tensorcontraction()
The matrix trace is equivalent to the contraction of a rank-2 array
Matrix product is equivalent to a tensor product of two rank-2 arrays, followed by a contraction of the 2nd and 3rd axes (in Python indexing axes number 1, 2). 