Idempotency

LinearAlgebra

For a Matrix $\mathbf{A}$, if

$${\mathbf{A}}^2=\mathbf{A}\times \mathbf{A}=\mathbf{A}$$

we call it Idempotency.

In other words,

$$f(f(x))=f(x)$$

also shows Idempotency.