Bugfixes for statespace/models/structural.py (#287)

Expand test coverage fix bugs in `structural.py`

docs/statespace/models.rst

@@ -6,7 +6,7 @@ Statespace Models
 .. autosummary::
    :toctree: generated
 
-    BayesianARIMA
+    BayesianSARIMA
     BayesianVARMAX
 
 *********************

docs/statespace/models/structural.rst

@@ -11,6 +11,4 @@ Structural Components
    TimeSeasonality
    FrequencySeasonality
    MeasurementError
-
-   StructuralTimeSeries
-   Component
+   CycleComponent

pymc_experimental/__init__.py

@@ -23,7 +23,7 @@
         handler = logging.StreamHandler()
         _log.addHandler(handler)
 
-from pymc_experimental import distributions, gp, utils
+from pymc_experimental import distributions, gp, statespace, utils
 from pymc_experimental.inference.fit import fit
 from pymc_experimental.model.marginal_model import MarginalModel
 from pymc_experimental.model.model_api import as_model

pymc_experimental/statespace/core/statespace.py

@@ -636,6 +636,37 @@ def _insert_random_variables(self) -> List[Variable]:
         }
         self.subbed_ssm = graph_replace(matrices, replace=replacement_dict, strict=True)
 
+    def _register_matrices_with_pymc_model(self) -> List[pt.TensorVariable]:
+        """
+        Add all statespace matrices to the PyMC model currently on the context stack as pm.Deterministic nodes, and
+        adds named dimensions if they are found.
+
+        Returns
+        -------
+        registered_matrices: list of pt.TensorVariable
+            List of statespace matrices, wrapped in pm.Deterministic
+        """
+
+        pm_mod = modelcontext(None)
+        matrices = self.unpack_statespace()
+
+        registered_matrices = []
+        for i, (matrix, name) in enumerate(zip(matrices, MATRIX_NAMES)):
+            time_varying_ndim = 2 if name in VECTOR_VALUED else 3
+            if not getattr(pm_mod, name, None):
+                shape, dims = self._get_matrix_shape_and_dims(name)
+                has_dims = dims is not None
+
+                if matrix.ndim == time_varying_ndim and has_dims:
+                    dims = (TIME_DIM,) + dims
+
+                x = pm.Deterministic(name, matrix, dims=dims)
+                registered_matrices.append(x)
+            else:
+                registered_matrices.append(matrices[i])
+
+        return registered_matrices
+
     def add_exogenous(self, exog: pt.TensorVariable) -> None:
         """
         Add an exogenous process to the statespace model
@@ -746,7 +777,6 @@ def build_statespace_graph(
         pm_mod = modelcontext(None)
 
         self._insert_random_variables()
-        matrices = self.unpack_statespace()
         obs_coords = pm_mod.coords.get(OBS_STATE_DIM, None)
 
         self.data_len = data.shape[0]
@@ -758,20 +788,7 @@ def build_statespace_graph(
             missing_fill_value=missing_fill_value,
         )
 
-        registered_matrices = []
-        for i, (matrix, name) in enumerate(zip(matrices, MATRIX_NAMES)):
-            time_varying_ndim = 2 if name in VECTOR_VALUED else 3
-            if not getattr(pm_mod, name, None):
-                shape, dims = self._get_matrix_shape_and_dims(name)
-                has_dims = dims is not None
-
-                if matrix.ndim == time_varying_ndim and has_dims:
-                    dims = (TIME_DIM,) + dims
-
-                x = pm.Deterministic(name, matrix, dims=dims)
-                registered_matrices.append(x)
-            else:
-                registered_matrices.append(matrices[i])
+        registered_matrices = self._register_matrices_with_pymc_model()
 
         filter_outputs = self.kalman_filter.build_graph(
             pt.as_tensor_variable(data),

pymc_experimental/statespace/filters/distributions.py

@@ -10,6 +10,7 @@
 from pytensor.graph.basic import Node
 
 floatX = pytensor.config.floatX
+COV_ZERO_TOL = 0
 
 lgss_shape_message = (
     "The LinearGaussianStateSpace distribution needs shape information to be constructed. "
@@ -157,8 +158,11 @@ def step_fn(*args):
             middle_rng, a_innovation = pm.MvNormal.dist(mu=0, cov=Q, rng=rng).owner.outputs
             next_rng, y_innovation = pm.MvNormal.dist(mu=0, cov=H, rng=middle_rng).owner.outputs
 
-            a_next = c + T @ a + R @ a_innovation
-            y_next = d + Z @ a_next + y_innovation
+            a_mu = c + T @ a
+            a_next = pt.switch(pt.all(pt.le(Q, COV_ZERO_TOL)), a_mu, a_mu + R @ a_innovation)
+
+            y_mu = d + Z @ a_next
+            y_next = pt.switch(pt.all(pt.le(H, COV_ZERO_TOL)), y_mu, y_mu + y_innovation)
 
             next_state = pt.concatenate([a_next, y_next], axis=0)
 
@@ -168,7 +172,11 @@ def step_fn(*args):
         Z_init = Z_ if Z_ in non_sequences else Z_[0]
         H_init = H_ if H_ in non_sequences else H_[0]
 
-        init_y_ = pm.MvNormal.dist(Z_init @ init_x_, H_init, rng=rng)
+        init_y_ = pt.switch(
+            pt.all(pt.le(H_init, COV_ZERO_TOL)),
+            Z_init @ init_x_,
+            pm.MvNormal.dist(Z_init @ init_x_, H_init, rng=rng),
+        )
         init_dist_ = pt.concatenate([init_x_, init_y_], axis=0)
 
         statespace, updates = pytensor.scan(
@@ -216,6 +224,7 @@ def __new__(
         steps=None,
         mode=None,
         sequence_names=None,
+        k_endog=None,
         **kwargs,
     ):
         dims = kwargs.pop("dims", None)
@@ -239,11 +248,29 @@ def __new__(
             sequence_names=sequence_names,
             **kwargs,
         )
-
         k_states = T.type.shape[0]
 
-        latent_states = latent_obs_combined[..., :k_states]
-        obs_states = latent_obs_combined[..., k_states:]
+        if k_endog is None and k_states is None:
+            raise ValueError("Could not infer number of observed states, explicitly pass k_endog.")
+        if k_endog is not None and k_states is not None:
+            total_shape = latent_obs_combined.type.shape[-1]
+            inferred_endog = total_shape - k_states
+            if inferred_endog != k_endog:
+                raise ValueError(
+                    f"Inferred k_endog does not agree with provided value ({inferred_endog} != {k_endog}). "
+                    f"It is not necessary to provide k_endog when the value can be inferred."
+                )
+            latent_slice = slice(None, -k_endog)
+            obs_slice = slice(-k_endog, None)
+        elif k_endog is None:
+            latent_slice = slice(None, k_states)
+            obs_slice = slice(k_states, None)
+        else:
+            latent_slice = slice(None, -k_endog)
+            obs_slice = slice(-k_endog, None)
+
+        latent_states = latent_obs_combined[..., latent_slice]
+        obs_states = latent_obs_combined[..., obs_slice]
 
         latent_states = pm.Deterministic(f"{name}_latent", latent_states, dims=latent_dims)
         obs_states = pm.Deterministic(f"{name}_observed", obs_states, dims=obs_dims)