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don't allow same seed for multiple chains in runMCMC
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#1494
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@paciorek @perrydv Of course I welcome discussion on this. But I feel somewhat strongly that one should be able to have this behaviour as currently provided: provide A few alternatives I can imagine:
Thoughts? |
Option 1 seems somewhat reasonable. But I wonder if maybe what we should do is that if a user provides a single number that that is the seed for the first chain and then the other chains use the random number sequence as it is, without setting a seed at all. |
@paciorek I can understand the idea of "if a user provides a single number that that is the seed for the first chain and then the other chains use the random number sequence as it is, without setting a seed at all.", except the fundamental inconsistency this would introduce with the (suggestion 1 again) Maybe just disallow the use of a single number for
That said, I personally still think it's a useful case to provide a single numeric seed, which is used as the starting seed for each chain. Admitting also, this case can be covered via |
Good point -- I hadn't thought about that inconsistency. I think we might think about the seed differently as often people run code without setting it and just leave things to pick up where the generator has left off. But I agree it feels a bit odd. So I'm happy with the idea of requiring as many seeds as chains if the user is providing a numeric value. |
Based on a user question, we've seen that using different initial values but same seed for chains where the model is fully conjugate results in identical samples (after a very short phase of alignment in the initial samples).
Perhaps in
runMCMC
we should not allow use of a single seed (or we should use that seed to generate multiple seeds to use in starting the chains.The text was updated successfully, but these errors were encountered: