I know that this is a very general question but I'm struggling to understand.. What does this probability notation mean?


This should be the probability over some set, but what does it mean to calculate the probability over a specific set? I mean, the probability should be of an event, so how could it be in respect to different sets?...

For example, I encountered it here in the wiki article about universal hashing: https://en.wikipedia.org/wiki/Universal_hashing#Mathematical_guarantees

$$Pr_{h\in{H}}(h(x) = h(y))$$

Same question for the similar notation of expected value in respect to a set: $E_{set}(variable)$...

  • 2
    $\begingroup$ Not familiar with the notation, but maybe $P_{S}(A)=P(A\mid S)=P(A\cap S)/P(S)$? Defined like this $P_S$ is a probability measure. $\endgroup$ – drhab Aug 30 '19 at 8:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.