Does this algorithm guarantee equaprobable outcomes?

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The algorithm described does not guarantee equaprobable outcomes for the numbers in the list, as the last number has a 50% probability of being selected. Each number has a probability that is half that of its successor, except for the first number, which has the same probability as the last. Suggestions for achieving equaprobability include generating a random number directly to select an element from the list instead of using coin flips. Coin flips are not inherently equiprobable in this context. The discussion highlights the need for a different approach to ensure equal selection probability among all numbers.
Bipolarity
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Suppose you have a list of numbers, say ##{1, 7, 9, 4, 5, 6}##.
You store the first number, and then iterate through this list.
For each number in the list, you flip a coin. If it is heads, you swap that element in the list with the number you stored. If tails, you do nothing. Either way, you move on to the next number in the list.

When you finish traversing the list, the resulting number is the number you stored. I am curious if all numbers in the list are equaprobably to be the final stored number, and if this is indeed the case, how might one prove this?

Thanks!

BiP
 
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No, the numbers are not equiprobable. The last number has a 50 % probability.
 
Ah I see, I suppose then that each number has half the probability of its successor?

Also, do you think there might be a way for me to tweak this so that the numbers are indeed equaprobable? This is for an application I'm trying to build.

BiP
 
Last edited:
Bipolarity said:
Ah I see, I suppose then that each number has half the probability of its successor?

Yes, apart from the first number which has the same.

Bipolarity said:
Also, do you think there might be a way for me to tweak this so that the numbers are indeed equaprobable? This is for an application I'm trying to build.
Yes, but the normal thing to do would be to simply generate a random number k between 1 and N, where N is the number of numbers you have and then select the kth number.
 
Coin flips aren't equiprobable , are they ?

ETA: never mind, I see the thread already :P
 
I was reading documentation about the soundness and completeness of logic formal systems. Consider the following $$\vdash_S \phi$$ where ##S## is the proof-system making part the formal system and ##\phi## is a wff (well formed formula) of the formal language. Note the blank on left of the turnstile symbol ##\vdash_S##, as far as I can tell it actually represents the empty set. So what does it mean ? I guess it actually means ##\phi## is a theorem of the formal system, i.e. there is a...

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