Th-Matrix is the "Identity Matrix", which is a matrix of multiplicative identity, and has a few special properties:
1) It can be multiplied by the left or right by a same dimensional matrix, but remains the same:
I*A = A*I = A

2) If the product of two matrices A and B is an Identity Matrix, these two matrices are mutually inverse to each other:
If A*B = B*A = I, then
A = B^-1, and B = A^-1