docs(sample_smc): describe the start parameter format#8310
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Closes pymc-devs#7283. Clarifies that for sample_smc the `start` argument is a starting *population* (one particle per draw), not a single starting point as in pm.sample, and shows the expected dict shape and key names. Specifically: - distinguishes the three accepted forms (None, dict, sequence of dict) and notes that the sequence length must equal `chains`; - documents that each dict maps the model's free-RV *value-variable* names to arrays of shape (draws, *var.shape), and that automatic transforms (e.g. log for HalfNormal) are reflected in the value-var names; - adds a self-contained example that sets a custom starting population for a Normal/HalfNormal model. No code or behavioral change. Co-authored-by: Cursor <cursoragent@cursor.com>
Documentation build overview
3 files changed± glossary.html± api/generated/pymc.smc.sample_smc.html± _modules/pymc/smc/sampling.html |
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Description
Closes #7283.
The
startargument ofpymc.sample_smcworks differently fromstartinpymc.sample, but the docstring did not actually explain how — it only said it is "a list of dict with lengthchains". The issue asked specifically for a clear description of the dict format.What this PR does
Rewrites the
startentry in thesample_smcdocstring to spell out:drawsparticles, not a single point per chain.None,dict, sequence ofdict) and the validation rule that the sequence length must equalchains.model.rvs_to_values[rv].name), and each value is an array of shape(draws, *var.shape)where rowiis particlei.pm.HalfNormal(\"sigma\")becomes\"sigma_log__\"), so starting values for such variables are expected on the unconstrained scale.Normal/HalfNormalmodel.I tried to keep the example minimal so it stays in sync with the actual contract used by
_initialize_kernelinpymc/smc/kernels.py.What this PR does not do
No code or behavioral change — docstring-only edit on
pymc.sample_smc. If maintainers prefer a different format (e.g. a dedicated subsection in the SMC docs or a User Guide page), happy to move the content.Related Issue(s)
Closes #7283
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