https://en.wikipedia.org/wiki/Bias%E2%80%93variance_tradeoff#Derivation
well,in the "Derivation" part of the wiki link.
i don't figure out why $E(f)=f$, does it imply that the function $f$ is constant?(but it makes no sense.)
thanks in advance.
https://en.wikipedia.org/wiki/Bias%E2%80%93variance_tradeoff#Derivation
well,in the "Derivation" part of the wiki link.
i don't figure out why $E(f)=f$, does it imply that the function $f$ is constant?(but it makes no sense.)
thanks in advance.
In the derivation part of wikipedia, the function is deterministic which means given a particular input in its domain, will always produce same output. So, we can take the function as constant given its domain.
We talk about expectation of a random variable, when we are doubtful about its outcome. Eg: It may or may not rain. So, when we say that it is expected to rain, We mean that most probably it will rain... but it may not also.
In the above situation, $f(x)$ is a pre-determined function. Value of $f(x)$ at $x$ is surely unique. So, the expectation of 'what might be the value of $f(x)$ is that it is surely $f(x)$.
I hope I am clear.