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[wiki] Error in Proof Of Stake FAQ (wrong EV calculation) #619

Closed ymsaid closed 4 years ago

ymsaid commented 6 years ago

In the nothing at stake problem section of the FAQ, there is an example explaining the consequences of a strategy punishing the validator for validating the wrong chain. In the diagram here https://github.com/vbuterin/diagrams/blob/master/slasher2sec.png the EV of only voting for A is shown as EV = 0.9 when it should be EV = 0.9 - 0.1*5 = 0.4. Basically if chain A has a p=0.9 chance of being the correct at the time of making the decision, the state of the world where B is the right decision (p=0.1) must be taken into account.

This is an important detail, because it shows why the penalty cannot exceed a certain limit relative to reward without breaking the participation constraint (every validator is better off not validating any chain). This discussion should probably be added to the associated paragraph.

In the particular example of the paragraph, the maximum penalty is 9. After that point, even choosing the most likely chain is not worth the trouble (EV <=0). More generally, an increase in the level of confusion in the network (measured by the number of concurrent chains) combined with a large penalty risks halting all validations.

cc @vbuterin

jamesray1 commented 5 years ago

Please see https://github.com/ethereum/wiki/blob/master/ISSUE_TEMPLATE.md.

gin commented 5 years ago

Question about PR process: When updating the diagram for this issue, should the PR be on https://github.com/vbuterin/diagrams/ or should the PR be on this repository (https://github.com/ethereum/wiki.wiki.git) where the updated diagram is pushed to here (with the link updated in the Markdown)?

ChrisChinchilla commented 5 years ago

@gin Good question! I'd say, attach a copy of the image to your PR and we'll figure out where to move it to.

hjlee9182 commented 5 years ago

@gin https://github.com/ethereum/wiki.wiki.git This address was 404 Found, Is it right?

ChrisChinchilla commented 5 years ago

Err, assuming you are tackling this issue (https://github.com/ethresearch/eth-wiki/issues/19), then PRs should be to the eth-wiki repo, as we're slowly migrating there.

ChrisChinchilla commented 4 years ago

This issue is being handled elsewhere