Overview#Identity Function also called an identity relation or identity map or identity transformation, is a function that always returns the same value that was used as its argument.
In equations, the function is given by f(x) = x.
Formally, if M is a set, the Identity Function f on M is defined to be that function with domain and codomain M which satisfies
f(x) = x for all elements x in M.
In other words, the function value f(x) in M is always the same input element x of M .