Add propose/accept/reject logic to prior_samples sampler

[danielturek]

This adds MH propose/accept/reject logic for the prior_samples sampler.

There is no longer an option for "sequential" draws from the provided samples, but rather on every MCMC iteration, a random draw from the provided samples is used as the proposal value(s).

[perrydv]

This looks good to me.
It would be an easy extension to allow a vector of weights to be provided as well, with draws proportion to weights.
We are trying keep the next release really minimal and practical, but I am noting this for discussion.

[danielturek]

@paciorek Are you able to re-generate the MCMC gold file using this branch prior_samples2? I think that's the only issue with test-mcmc.R.

[paciorek]

Yes, I can look at that.

[paciorek]

@danielturek just to make sure....

Previously in the gold file, I see this pertaining to prior_samples sampler:

"""
[Note] prior_samples sampler will recycle sequential draws from prior samples, since 10 samples were provided, and 11 MCMC iterations will be run.
[Note] prior_samples sampler will recycle sequential draws from prior samples, since 3 samples were provided, and 11 MCMC iterations will be run.
"""

Now when I manually run lines 2888-2931, I only see:

"""
[Warning] No samplers assigned for 1 node, use conf$getUnsampledNodes() for node name.
"""

Is that what you expect? I guess the omission of the previous message makes sense given the new correct behavior, but I don't understand why the "No samplers" message would only now appear in the last MCMC configuration where 'b' is not assigned a sampler.

[danielturek]

@paciorek Yes, this looks correct to me. The MCMC configuration created on line 2926 specifies nodes = NULL, so no samplers are assigned by default. Then samplers are manually added for a and c, but not for b. So issuing this warning (from line 2929) makes sense to me. In all the cases preceding that one, the MCMC configuration by default assigns samplers to all nodes, so such a warning is never issued. Does this make sense?