Improve ptemcee

This is a total rewrite of the ptemcee implementation. Originally, we had based ptemcee on emcee, but emcee has changed quite significantly and I anticipate it will be easier to maintain the two uncoupled from hereon. This adds sufficient functionality to ptemcee for it to be usable on gravitational wave events. Here is a summary of the changes

1. Add automatic convergence to the user interface: users now specify nsamples as a the primary input. The sampler will run until it has nsamples independent samples from the posterior. The user now has access to a reduced set of the ptemcee full functionality (e.g. iterations), but this isn't required given the convergence checking.
2. Add diagnostic plots for the autocorrelation time, e.g.:
3. Improve the traceplots to show the convergence and the current posterior samples
4. Add dumping of posterior samples to a .dat file
5. Add multi-processing support, tested on a 16 core machine to give a significant reduction in compute time (exact timings yet to be calculated).
6. Add regular 10-minute checkpointing

Note, I have intentionally put much of the primary logic into functions rather than class methods. This is because eventually we should port changes to parallel bilby and potentially other samplers and this is most easily done from a functional interface (at least for parallel bilby where inheritance causes issues with the parallel aspects).

bilby/core/sampler/ptemcee.py

@@ -47,7 +47,7 @@ class Ptemcee(MCMCSampler):
     def __init__(self, likelihood, priors, outdir='outdir', label='label',
                  use_ratio=False, plot=False, skip_import_verification=False,
                  resume=True, nsamples=5000, burn_in_nact=50, thin_by_nact=1,
-                 autocorr_c=5, safety=1, ncheck=50, nfrac=5, frac_threshold=0.01,
+                 autocorr_c=5, safety=1, frac_threshold=0.01,
                  autocorr_tol=50, min_tau=1, check_point_deltaT=600, 
                  threads=1, **kwargs):
         super(Ptemcee, self).__init__(
@@ -60,12 +60,10 @@ class Ptemcee(MCMCSampler):
         signal.signal(signal.SIGALRM, self.write_current_state_and_exit)
 
         self.resume = resume
-        self.ncheck = ncheck
         self.autocorr_c = autocorr_c
         self.safety = safety
         self.burn_in_nact = burn_in_nact
         self.thin_by_nact = thin_by_nact
-        self.nfrac = nfrac
         self.frac_threshold = frac_threshold
         self.nsamples = nsamples
         self.autocorr_tol = autocorr_tol
@@ -94,55 +92,75 @@ class Ptemcee(MCMCSampler):
                  for _ in range(self.sampler_init_kwargs["nwalkers"])]
                 for _ in range(self.kwargs['ntemps'])]
 
-    def get_sampler(self):
+    def setup_sampler(self):
         import ptemcee
         if os.path.isfile(self.resume_file) and self.resume is True:
             logger.info("Resume data {} found".format(self.resume_file))
             with open(self.resume_file, "rb") as file:
                 data = dill.load(file)
+
             self.sampler = data["sampler"]
-            self.sampler.pool = None
             self.tau_list = data["tau_list"]
             self.tau_list_n = data["tau_list_n"]
+            self.time_per_check = data["time_per_check"]
+
+            self.sampler.pool = self.pool
+            self.sampler.threads = self.threads
+
             pos0 = None
+
             logger.info("Resuming from previous run with time={}".format(self.sampler.time))
 
         else:
+            # Initialize the PTSampler
             self.sampler = ptemcee.Sampler(
                 dim=self.ndim, logl=do_nothing_function, logp=do_nothing_function,
                 pool=self.pool, threads=self.threads, **self.sampler_init_kwargs)
+
+            # Overwrite the _likeprior to improve performance with threads > 1
             self.sampler._likeprior = LikePriorEvaluator(
                 self.search_parameter_keys, use_ratio=self.use_ratio)
+
+            # Set up empty lists
+            self.tau_list = []
+            self.tau_list_n = []
+            self.time_per_check = []
+
+            # Initialize the walker postitions
             pos0 = self.get_pos0_from_prior()
 
         return self.sampler, pos0
 
-    def run_sampler(self):
-        import schwimmbad
+    def setup_pool(self):
         if self.threads > 1:
+            import schwimmbad
             logger.info("Creating MultiPool with {} processes".format(self.threads))
-            with schwimmbad.MultiPool(self.threads, initializer=init,
-                                      initargs=(self.likelihood, self.priors)) as pool:
-                self.pool = pool
-                return self.run_sampler_internal()
+            self.pool = schwimmbad.MultiPool(
+                self.threads,
+                initializer=init,
+                initargs=(self.likelihood, self.priors))
         else:
             self.pool = None
-            return self.run_sampler_internal()
+
+    def run_sampler(self):
+        self.setup_pool()
+        out = self.run_sampler_internal()
+        if self.pool:
+            self.pool.close()
+        return out
 
     def run_sampler_internal(self):
         import emcee
-        sampler, pos0 = self.get_sampler()
-        self.time_per_check = []
-        self.tau_list = []
-        self.tau_list_n = []
+        sampler, pos0 = self.setup_sampler()
 
         t0 = datetime.datetime.now()
         logger.info("Starting to sample")
         for (pos0, lnprob, lnlike) in sampler.sample(
                 pos0, **self.sampler_function_kwargs):
-            # Only check convergence every ncheck steps
-            if sampler.time % self.ncheck:
-                continue
+
+            # Calculate time per iteration
+            self.time_per_check.append((datetime.datetime.now() - t0).total_seconds())
+            t0 = datetime.datetime.now()
 
             # Compute ACT tau for 0-temperature chains
             samples = sampler.chain[0, :, : sampler.time, :]
@@ -163,49 +181,53 @@ class Ptemcee(MCMCSampler):
             # Apply multiplicitive safety factor
             tau = self.safety * np.mean(taus)
 
-            if np.isnan(tau) or np.isinf(tau):
-                print("{} | Unable to use tau={}".format(sampler.time, tau), flush=True)
-                continue
-
-            # Convert to an integer and store for plotting
-            tau = int(tau)
+            # Store for convergence checking and plotting
             self.tau_list.append(tau)
             self.tau_list_n.append(sampler.time)
 
+            # Convert to an integer
+            tau = int(np.floor(tau)) if not np.isnan(tau) else tau
+
+            if np.isnan(tau) or np.isinf(tau):
+                print_progress(
+                    self.sampler,
+                    self.time_per_check,
+                    self.nsamples,
+                    np.nan,
+                    np.nan,
+                    np.nan,
+                    False)
+                continue
+
             # Calculate the effective number of samples available
             self.nburn = int(self.burn_in_nact * tau)
             self.thin = int(np.max([1, self.thin_by_nact * tau]))
-            samples_per_check = self.ncheck * sampler.nwalkers / self.thin
+            samples_per_check = sampler.nwalkers / self.thin
             self.nsamples_effective = int(sampler.nwalkers * (sampler.time - self.nburn) / self.thin)
 
-            # Calculate fractional change in tau from previous iteration
-            frac = (tau - np.array(self.tau_list)[-self.nfrac - 1: -1]) / tau
-            passes = frac < self.frac_threshold
-
             # Calculate convergence boolean
             converged = self.nsamples < self.nsamples_effective
-            converged &= np.all(passes)
-            if sampler.time < tau * self.autocorr_tol or tau < self.min_tau:
-                converged = False
-                tau_pass = False
+
+            # Calculate fractional change in tau from previous iteration
+            check_taus = np.array(self.tau_list[-tau * self.autocorr_tol:])
+            if not np.any(np.isnan(check_taus)):
+                frac = (tau - check_taus) / tau
+                tau_usable = np.all(frac < self.frac_threshold)
             else:
-                tau_pass = True
+                tau_usable = False
 
-            # Calculate time per iteration
-            self.time_per_check.append((datetime.datetime.now() - t0).total_seconds())
-            t0 = datetime.datetime.now()
+            if sampler.time < tau * self.autocorr_tol or tau < self.min_tau:
+                tau_usable = False
 
             # Print an update on the progress
             print_progress(
                 self.sampler,
-                self.ncheck,
                 self.time_per_check,
                 self.nsamples,
                 self.nsamples_effective,
                 samples_per_check,
-                passes,
                 tau,
-                tau_pass,
+                tau_usable,
             )
 
             if converged:
@@ -219,7 +241,7 @@ class Ptemcee(MCMCSampler):
                 last_checkpoint_s = np.sum(self.time_per_check)
 
             if last_checkpoint_s > self.check_point_deltaT:
-                self.write_current_state()
+                self.write_current_state(plot=self.plot)
 
         # Check if we reached the end without converging
         if sampler.time == self.sampler_function_kwargs["iterations"]:
@@ -230,7 +252,7 @@ class Ptemcee(MCMCSampler):
             )
 
         # Run a final checkpoint to update the plots and samples
-        self.write_current_state()
+        self.write_current_state(plot=self.plot)
 
         # Get 0-likelihood samples and store in the result
         samples = sampler.chain[0, :, :, :]  # nwalkers, nsteps, ndim
@@ -257,26 +279,37 @@ class Ptemcee(MCMCSampler):
 
     def write_current_state_and_exit(self, signum=None, frame=None):
         logger.warning("Run terminated with signal {}".format(signum))
-        self.write_current_state()
+        if getattr(self, 'pool', None):
+            self.write_current_state(plot=False)
+            logger.warning("Closing pool")
+            self.pool.close()
         sys.exit(77)
 
-    def write_current_state(self):
+    def write_current_state(self, plot=True):
         checkpoint(self.outdir, self.label, self.nsamples_effective,
                    self.sampler, self.nburn, self.thin,
                    self.search_parameter_keys, self.resume_file, self.tau_list,
-                   self.tau_list_n)
+                   self.tau_list_n, self.time_per_check)
+
+        if plot:
+            # Generate the walkers plot diagnostic
+            plot_walkers(
+                self.sampler.chain[0, :, : self.sampler.time, :],
+                self.nburn, self.search_parameter_keys, self.outdir, self.label
+            )
+
+            # Generate the tau plot diagnostic
+            plot_tau(self.tau_list_n, self.tau_list, self.outdir, self.label)
 
 
 def print_progress(
     sampler,
-    ncheck,
     time_per_check,
     nsamples,
     nsamples_effective,
     samples_per_check,
-    passes,
     tau,
-    tau_pass,
+    tau_usable,
 ):
     # Setup acceptance string
     acceptance = sampler.acceptance_fraction[0, :]
@@ -290,30 +323,31 @@ def print_progress(
 
     ave_time_per_check = np.mean(time_per_check[-3:])
     time_left = (
-        (nsamples - nsamples_effective)
-        * ave_time_per_check
-        / samples_per_check
+        (nsamples - nsamples_effective) * ave_time_per_check / samples_per_check
     )
     if time_left > 0:
         time_left = str(datetime.timedelta(seconds=int(time_left)))
     else:
         time_left = "waiting on convergence"
 
-    convergence = "".join([["F", "T"][i] for i in passes])
+    sampling_time = datetime.timedelta(seconds=np.sum(time_per_check))
 
     tau_str = str(tau)
-    if tau_pass is False:
-        tau_str = tau_str + "(F)"
+    if tau_usable is False:
+        tau_str = "!{}".format(tau_str)
+    else:
+        tau_str = "={}".format(tau_str)
 
-    evals_per_check = sampler.nwalkers * sampler.ntemps * ncheck
+    evals_per_check = sampler.nwalkers * sampler.ntemps
 
     ncalls = "{:1.1e}".format(sampler.time * sampler.nwalkers * sampler.ntemps)
     eval_timing = "{:1.1f}ms/evl".format(1e3 * ave_time_per_check / evals_per_check)
     samp_timing = "{:1.2f}ms/smp".format(1e3 * ave_time_per_check / samples_per_check)
 
     print(
-        "{}| nc:{}| a0:{}| swp:{}| n:{}<{}| tau:{}| {}| {}| {}".format(
+        "{}| {} | nc:{}| a0:{}| swp:{}| n:{}<{}| tau{}| {}| {}".format(
             sampler.time,
+            str(sampling_time).split(".")[0],
             ncalls,
             acceptance_str,
             tswap_acceptance_str,
@@ -322,14 +356,14 @@ def print_progress(
             tau_str,
             eval_timing,
             samp_timing,
-            convergence,
         ),
         flush=True,
     )
 
 
 def checkpoint(outdir, label, nsamples_effective, sampler, nburn, thin,
-               search_parameter_keys, resume_file, tau_list, tau_list_n):
+               search_parameter_keys, resume_file, tau_list, tau_list_n,
+               time_per_check):
     logger.info("Writing checkpoint and diagnostics")
     ndim = sampler.dim
 
@@ -349,20 +383,17 @@ def checkpoint(outdir, label, nsamples_effective, sampler, nburn, thin,
     sampler_copy._logposterior = sampler._logposterior[:, :, : sampler.time]
     sampler_copy._loglikelihood = sampler._loglikelihood[:, :, : sampler.time]
     sampler_copy._beta_history = sampler._beta_history[:, : sampler.time]
-    data = dict(sampler=sampler_copy, tau_list=tau_list, tau_list_n=tau_list_n)
+
+    data = dict(
+        sampler=sampler_copy, tau_list=tau_list, tau_list_n=tau_list_n,
+        time_per_check=time_per_check)
+
     with open(resume_file, "wb") as file:
         dill.dump(data, file, protocol=4)
     del data, sampler_copy
 
-    # Generate the walkers plot diagnostic
-    plot_walkers(
-        sampler.chain[0, :, : sampler.time, :], nburn, search_parameter_keys, outdir, label
-    )
-
-    # Generate the tau plot diagnostic
-    plot_tau(tau_list_n, tau_list, outdir, label)
 
-    logger.info("Finished writing checkpoint and diagnostics")
+    logger.info("Finished writing checkpoint")
 
 
 def plot_walkers(walkers, nburn, parameter_labels, outdir, label):
@@ -388,7 +419,7 @@ def plot_walkers(walkers, nburn, parameter_labels, outdir, label):
 
 def plot_tau(tau_list_n, tau_list, outdir, label):
     fig, ax = plt.subplots()
-    ax.plot(tau_list_n, tau_list, "-x")
+    ax.plot(tau_list_n, tau_list, "-")
     ax.set_xlabel("Iteration")
     ax.set_ylabel(r"$\langle \tau \rangle$")
     fig.savefig("{}/{}_tau.png".format(outdir, label))