Refactor HMC and warning system

pymc3/backends/base.py

@@ -4,12 +4,16 @@
 creating custom backends).
 """
 import itertools as itl
+import logging
 
 import numpy as np
 import warnings
 import theano.tensor as tt
 
 from ..model import modelcontext
+from .report import SamplerReport, merge_reports
+
+logger = logging.getLogger('pymc3')
 
 
 class BackendError(Exception):
@@ -61,6 +65,10 @@ def __init__(self, name, model=None, vars=None, test_point=None):
         self.chain = None
         self._is_base_setup = False
         self.sampler_vars = None
+        self._warnings = []
+
+    def _add_warnings(self, warnings):
+        self._warnings.extend(warnings)
 
     # Sampling methods
 
@@ -174,7 +182,7 @@ def get_sampler_stats(self, varname, sampler_idx=None, burn=0, thin=1):
             return self._get_sampler_stats(varname, sampler_idx, burn, thin)
 
         sampler_idxs = [i for i, s in enumerate(self.sampler_vars)
-                       if varname in s]
+                        if varname in s]
         if not sampler_idxs:
             raise KeyError("Unknown sampler stat %s" % varname)
 
@@ -185,20 +193,19 @@ def get_sampler_stats(self, varname, sampler_idx=None, burn=0, thin=1):
         else:
             return vals
 
-
     def _get_sampler_stats(self, varname, sampler_idx, burn, thin):
         """Get sampler statistics."""
         raise NotImplementedError()
 
     def _slice(self, idx):
         """Slice trace object."""
-        raise NotImplementedError
+        raise NotImplementedError()
 
     def point(self, idx):
         """Return dictionary of point values at `idx` for current chain
         with variables names as keys.
         """
-        raise NotImplementedError
+        raise NotImplementedError()
 
     @property
     def stat_names(self):
@@ -258,6 +265,11 @@ def __init__(self, straces):
                 raise ValueError("Chains are not unique.")
             self._straces[strace.chain] = strace
 
+        self._report = SamplerReport()
+        for strace in straces:
+            if hasattr(strace, '_warnings'):
+                self._report._add_warnings(strace._warnings, strace.chain)
+
     def __repr__(self):
         template = '<{}: {} chains, {} iterations, {} variables>'
         return template.format(self.__class__.__name__,
@@ -271,6 +283,10 @@ def nchains(self):
     def chains(self):
         return list(sorted(self._straces.keys()))
 
+    @property
+    def report(self):
+        return self._report
+
     def __getitem__(self, idx):
         if isinstance(idx, slice):
             return self._slice(idx)
@@ -303,7 +319,7 @@ def __getitem__(self, idx):
         raise KeyError("Unknown variable %s" % var)
 
     _attrs = set(['_straces', 'varnames', 'chains', 'stat_names',
-                  'supports_sampler_stats'])
+                  'supports_sampler_stats', '_report'])
 
     def __getattr__(self, name):
         # Avoid infinite recursion when called before __init__
@@ -447,10 +463,13 @@ def get_sampler_stats(self, varname, burn=0, thin=1, combine=True,
                    for chain in chains]
         return _squeeze_cat(results, combine, squeeze)
 
-    def _slice(self, idx):
-        """Return a new MultiTrace object sliced according to `idx`."""
-        new_traces = [trace._slice(idx) for trace in self._straces.values()]
-        return MultiTrace(new_traces)
+    def _slice(self, slice):
+        """Return a new MultiTrace object sliced according to `slice`."""
+        new_traces = [trace._slice(slice) for trace in self._straces.values()]
+        trace = MultiTrace(new_traces)
+        idxs = slice.indices(len(self))
+        trace._report = self._report._slice(*idxs)
+        return trace
 
     def point(self, idx, chain=None):
         """Return a dictionary of point values at `idx`.
@@ -502,6 +521,7 @@ def merge_traces(mtraces):
             if new_chain in base_mtrace._straces:
                 raise ValueError("Chains are not unique.")
             base_mtrace._straces[new_chain] = strace
+    base_mtrace.report = merge_reports([trace.report for trace in mtraces])
     return base_mtrace
 
 

pymc3/backends/ndarray.py

@@ -116,8 +116,9 @@ def close(self):
         self.samples = {var: vtrace[:self.draw_idx]
                         for var, vtrace in self.samples.items()}
         if self._stats is not None:
-            self._stats = [{var: trace[:self.draw_idx] for var, trace in stats.items()}
-                           for stats in self._stats]
+            self._stats = [
+                {var: trace[:self.draw_idx] for var, trace in stats.items()}
+                for stats in self._stats]
 
     # Selection methods
 

pymc3/backends/report.py

@@ -0,0 +1,162 @@
+from collections import namedtuple
+import logging
+import enum
+
+
+logger = logging.getLogger('pymc3')
+
+
+@enum.unique
+class WarningType(enum.Enum):
+    # For HMC and NUTS
+    DIVERGENCE = 1
+    TUNING_DIVERGENCE = 2
+    DIVERGENCES = 3
+    TREEDEPTH = 4
+    # Problematic sampler parameters
+    BAD_PARAMS = 5
+    # Indications that chains did not converge, eg Rhat
+    CONVERGENCE = 6
+    BAD_ACCEPTANCE = 7
+
+
+SamplerWarning = namedtuple(
+    'SamplerWarning',
+    "kind, message, level, step, exec_info, extra")
+
+
+_LEVELS = {
+    'info': logging.INFO,
+    'error': logging.ERROR,
+    'warn': logging.WARN,
+    'debug': logging.DEBUG,
+    'critical': logging.CRITICAL,
+}
+
+
+class SamplerReport(object):
+    def __init__(self):
+        self._chain_warnings = {}
+        self._global_warnings = []
+        self._effective_n = None
+        self._gelman_rubin = None
+
+    @property
+    def _warnings(self):
+        chains = sum(self._chain_warnings.values(), [])
+        return chains + self._global_warnings
+
+    @property
+    def ok(self):
+        """Whether the automatic convergence checks found serious problems."""
+        return all(_LEVELS[warn.level] < _LEVELS['warn']
+                   for warn in self._warnings)
+
+    def raise_ok(self, level='error'):
+        errors = [warn for warn in self._warnings
+                  if _LEVELS[warn.level] >= _LEVELS[level]]
+        if errors:
+            raise ValueError('Serious convergence issues during sampling.')
+
+    def _run_convergence_checks(self, trace):
+        if trace.nchains == 1:
+            msg = ("Only one chain was sampled, this makes it impossible to "
+                   "run some convergence checks")
+            warn = SamplerWarning(WarningType.BAD_PARAMS, msg, 'info',
+                                  None, None, None)
+            self._add_warnings([warn])
+            return
+
+        from pymc3 import diagnostics
+
+        self._effective_n = effective_n = diagnostics.effective_n(trace)
+        self._gelman_rubin = gelman_rubin = diagnostics.gelman_rubin(trace)
+
+        warnings = []
+        rhat_max = max(val.max() for val in gelman_rubin.values())
+        if rhat_max > 1.4:
+            msg = ("The gelman-rubin statistic is larger than 1.4 for some "
+                   "parameters. The sampler did not converge.")
+            warn = SamplerWarning(
+                WarningType.CONVERGENCE, msg, 'error', None, None, gelman_rubin)
+            warnings.append(warn)
+        elif rhat_max > 1.2:
+            msg = ("The gelman-rubin statistic is larger than 1.2 for some "
+                   "parameters.")
+            warn = SamplerWarning(
+                WarningType.CONVERGENCE, msg, 'warn', None, None, gelman_rubin)
+            warnings.append(warn)
+        elif rhat_max > 1.05:
+            msg = ("The gelman-rubin statistic is larger than 1.05 for some "
+                   "parameters. This indicates slight problems during "
+                   "sampling.")
+            warn = SamplerWarning(
+                WarningType.CONVERGENCE, msg, 'info', None, None, gelman_rubin)
+            warnings.append(warn)
+
+        eff_min = min(val.min() for val in effective_n.values())
+        n_samples = len(trace) * trace.nchains
+        if eff_min < 200 and n_samples >= 500:
+            msg = ("The estimated number of effective samples is smaller than "
+                   "200 for some parameters.")
+            warn = SamplerWarning(
+                WarningType.CONVERGENCE, msg, 'error', None, None, effective_n)
+            warnings.append(warn)
+        elif eff_min / n_samples < 0.25:
+            msg = ("The number of effective samples is smaller than "
+                   "25% for some parameters.")
+            warn = SamplerWarning(
+                WarningType.CONVERGENCE, msg, 'warn', None, None, effective_n)
+            warnings.append(warn)
+
+        self._add_warnings(warnings)
+
+    def _add_warnings(self, warnings, chain=None):
+        if chain is None:
+            warn_list = self._global_warnings
+        else:
+            warn_list = self._chain_warnings.setdefault(chain, [])
+        warn_list.extend(warnings)
+
+    def _log_summary(self):
+
+        def log_warning(warn):
+            level = _LEVELS[warn.level]
+            logger.log(level, warn.message)
+
+        for chain, warns in self._chain_warnings.items():
+            for warn in warns:
+                log_warning(warn)
+        for warn in self._global_warnings:
+            log_warning(warn)
+
+    def _slice(self, start, stop, step):
+        report = SamplerReport()
+
+        def filter_warns(warnings):
+            filtered = []
+            for warn in warnings:
+                if warn.step is None:
+                    filtered.append(warn)
+                elif (start <= warn.step < stop and
+                        (warn.step - start) % step == 0):
+                    warn = warn._replace(step=warn.step - start)
+                    filtered.append(warn)
+            return filtered
+
+        report._add_warnings(filter_warns(self._global_warnings))
+        for chain in self._chain_warnings:
+            report._add_warnings(
+                filter_warns(self._chain_warnings[chain]),
+                chain)
+
+        return report
+
+
+def merge_reports(reports):
+    report = SamplerReport()
+    for rep in reports:
+        report._add_warnings(rep._global_warnings)
+        for chain in rep._chain_warnings:
+            report._add_warnings(rep._chain_warnings[chain], chain)
+    return report

pymc3/diagnostics.py

@@ -250,8 +250,8 @@ def get_neff(x, Vhat):
         if t % 2:
             t -= 1
 
-        return min(num_chains * num_samples,
-                   int(num_chains * num_samples / (1. + 2 * rho[1:t-1].sum())))
+        neff = num_chains * num_samples / (1. + 2 * rho[1:t-1].sum())
+        return min(num_chains * num_samples, np.floor(neff))
 
     def generate_neff(trace_values):
         x = np.array(trace_values)

pymc3/model.py

@@ -10,7 +10,7 @@
 from theano import theano, tensor as tt
 from theano.tensor.var import TensorVariable
 
-from pymc3.theanof import set_theano_conf
+from pymc3.theanof import set_theano_conf, floatX
 import pymc3 as pm
 from pymc3.math import flatten_list
 from .memoize import memoize, WithMemoization
@@ -1061,13 +1061,13 @@ def _get_scaling(total_size, shape, ndim):
     scalar
     """
     if total_size is None:
-        coef = pm.floatX(1)
+        coef = floatX(1)
     elif isinstance(total_size, int):
         if ndim >= 1:
             denom = shape[0]
         else:
             denom = 1
-        coef = pm.floatX(total_size) / pm.floatX(denom)
+        coef = floatX(total_size) / floatX(denom)
     elif isinstance(total_size, (list, tuple)):
         if not all(isinstance(i, int) for i in total_size if (i is not Ellipsis and i is not None)):
             raise TypeError('Unrecognized `total_size` type, expected '
@@ -1085,20 +1085,20 @@ def _get_scaling(total_size, shape, ndim):
             raise ValueError('Length of `total_size` is too big, '
                              'number of scalings is bigger that ndim, got %r' % total_size)
         elif (len(begin) + len(end)) == 0:
-            return pm.floatX(1)
+            return floatX(1)
         if len(end) > 0:
             shp_end = shape[-len(end):]
         else:
             shp_end = np.asarray([])
         shp_begin = shape[:len(begin)]
-        begin_coef = [pm.floatX(t) / shp_begin[i] for i, t in enumerate(begin) if t is not None]
-        end_coef = [pm.floatX(t) / shp_end[i] for i, t in enumerate(end) if t is not None]
+        begin_coef = [floatX(t) / shp_begin[i] for i, t in enumerate(begin) if t is not None]
+        end_coef = [floatX(t) / shp_end[i] for i, t in enumerate(end) if t is not None]
         coefs = begin_coef + end_coef
         coef = tt.prod(coefs)
     else:
         raise TypeError('Unrecognized `total_size` type, expected '
                         'int or list of ints, got %r' % total_size)
-    return tt.as_tensor(pm.floatX(coef))
+    return tt.as_tensor(floatX(coef))
 
 
 class FreeRV(Factor, TensorVariable):