Merge remote-tracking branch 'upstream/master'

Author: fonnesbeck

RELEASE-NOTES.md

@@ -1,11 +1,18 @@
 # Release Notes
 
 ## PyMC3 3.9.x (on deck)
+
+### Maintenance
+- Fix an error on Windows and Mac where error message from unpickling models did not show up in the notebook, or where sampling froze when a worker process crashed (see [#3991](https://github.com/pymc-devs/pymc3/pull/3991)).
+
 ### Documentation
 - Notebook on [multilevel modeling](https://docs.pymc.io/notebooks/multilevel_modeling.html) has been rewritten to showcase ArviZ and xarray usage for inference result analysis (see [#3963](https://github.com/pymc-devs/pymc3/pull/3963))
 
 ### New features
+- Introduce optional arguments to `pm.sample`: `mp_ctx` to control how the processes for parallel sampling are started, and `pickle_backend` to specify which library is used to pickle models in parallel sampling when the multiprocessing cnotext is not of type `fork`. (see [#3991](https://github.com/pymc-devs/pymc3/pull/3991))
 - Add sampler stats `process_time_diff`, `perf_counter_diff` and `perf_counter_start`, that record wall and CPU times for each NUTS and HMC sample (see [ #3986](https://github.com/pymc-devs/pymc3/pull/3986)).
+- Extend `keep_size` argument handling for `sample_posterior_predictive` and `fast_sample_posterior_predictive`, to work on arviz InferenceData and xarray Dataset input values. (see [PR #4006](https://github.com/pymc-devs/pymc3/pull/4006) and [Issue #4004](https://github.com/pymc-devs/pymc3/issues/4004).
+- SMC-ABC: add the wasserstein and energy distance functions. Refactor API, the distance, sum_stats and epsilon arguments are now passed `pm.Simulator` instead of `pm.sample_smc`. Add random method to `pm.Simulator`. Add option to save the simulated data. Improves LaTeX representation [#3996](https://github.com/pymc-devs/pymc3/pull/3996)
 
 ## PyMC3 3.9.2 (24 June 2020)
 ### Maintenance

docs/source/notebooks/SMC-ABC_Lotka-Volterra_example.ipynb

@@ -27,12 +27,6 @@
         handler = logging.StreamHandler()
         _log.addHandler(handler)
 
-# Set start method to forkserver for MacOS to enable multiprocessing
-# Closes issue https://github.com/pymc-devs/pymc3/issues/3849
-sys = platform.system()
-if sys == "Darwin":
-    new_context = mp.get_context("forkserver")
-
 
 def __set_compiler_flags():
     # Workarounds for Theano compiler problems on various platforms