In: Advanced Math
Let u be a unit vector, and P = Identity vector − u⊗u. Compute P^2 and P^(−1).
Hint: Rank one Matrix.
The outer product is equivalent to the matrix multiplication that is
where is the transpose of . Since is a unit vector,
Now,
is idempotent and which means is non-identity idempotent matrix.
Now we know that only non-singular idempotent matrix is the identity matrix. All the non-identity idempotent matrix are singular and hence does not invertible. So, does not exist in the present case.