Add gufunc_signature to SymbolicRandomVariables

pymc/distributions/censored.py

@@ -30,6 +30,8 @@ class CensoredRV(SymbolicRandomVariable):
     """Censored random variable"""
 
     inline_logprob = True
+    signature = "(),(),()->()"
+    ndim_supp = 0
     _print_name = ("Censored", "\\operatorname{Censored}")
 
 
@@ -115,7 +117,6 @@ def rv_op(cls, dist, lower=None, upper=None, size=None):
         return CensoredRV(
             inputs=[dist_, lower_, upper_],
             outputs=[censored_rv_],
-            ndim_supp=0,
         )(dist, lower, upper)
 
 

pymc/distributions/distribution.py

@@ -33,11 +33,13 @@
 from pytensor.graph.utils import MetaType
 from pytensor.scan.op import Scan
 from pytensor.tensor.basic import as_tensor_variable
+from pytensor.tensor.blockwise import safe_signature
 from pytensor.tensor.random.op import RandomVariable
 from pytensor.tensor.random.rewriting import local_subtensor_rv_lift
 from pytensor.tensor.random.type import RandomGeneratorType, RandomType
 from pytensor.tensor.random.utils import normalize_size_param
 from pytensor.tensor.rewriting.shape import ShapeFeature
+from pytensor.tensor.utils import _parse_gufunc_signature
 from pytensor.tensor.variable import TensorVariable
 from typing_extensions import TypeAlias
 
@@ -261,6 +263,12 @@ class SymbolicRandomVariable(OpFromGraph):
     (0 for scalar, 1 for vector, ...)
      """
 
+    ndims_params: Optional[Sequence[int]] = None
+    """Number of core dimensions of the distribution's parameters."""
+
+    signature: str = None
+    """Numpy-like vectorized signature of the distribution."""
+
     inline_logprob: bool = False
     """Specifies whether the logprob function is derived automatically by introspection
     of the inner graph.
@@ -271,9 +279,25 @@ class SymbolicRandomVariable(OpFromGraph):
     _print_name: tuple[str, str] = ("Unknown", "\\operatorname{Unknown}")
     """Tuple of (name, latex name) used for for pretty-printing variables of this type"""
 
-    def __init__(self, *args, ndim_supp, **kwargs):
-        """Initialitze a SymbolicRandomVariable class."""
-        self.ndim_supp = ndim_supp
+    def __init__(
+        self,
+        *args,
+        **kwargs,
+    ):
+        """Initialize a SymbolicRandomVariable class."""
+        if self.signature is None:
+            self.signature = kwargs.get("signature", None)
+
+        if self.signature is not None:
+            inputs_sig, outputs_sig = _parse_gufunc_signature(self.signature)
+            self.ndims_params = [len(sig) for sig in inputs_sig]
+            self.ndim_supp = max(len(out_sig) for out_sig in outputs_sig)
+
+        if self.ndim_supp is None:
+            self.ndim_supp = kwargs.get("ndim_supp", None)
+            if self.ndim_supp is None:
+                raise ValueError("ndim_supp or gufunc_signature must be provided")
+
         kwargs.setdefault("inline", True)
         super().__init__(*args, **kwargs)
 
@@ -286,6 +310,11 @@ def update(self, node: Node):
         """
         return {}
 
+    def batch_ndim(self, node: Node) -> int:
+        """Number of dimensions of the distribution's batch shape."""
+        out_ndim = max(getattr(out.type, "ndim", 0) for out in node.outputs)
+        return out_ndim - self.ndim_supp
+
 
 class Distribution(metaclass=DistributionMeta):
     """Statistical distribution"""
@@ -558,23 +587,29 @@ def dist(
         logcdf: Optional[Callable] = None,
         random: Optional[Callable] = None,
         support_point: Optional[Callable] = None,
-        ndim_supp: int = 0,
+        ndim_supp: Optional[int] = None,
         ndims_params: Optional[Sequence[int]] = None,
+        signature: Optional[str] = None,
         dtype: str = "floatX",
         class_name: str = "CustomDist",
         **kwargs,
     ):
+        if ndim_supp is None or ndims_params is None:
+            if signature is None:
+                ndim_supp = 0
+                ndims_params = [0] * len(dist_params)
+            else:
+                inputs, outputs = _parse_gufunc_signature(signature)
+                ndim_supp = max(len(out) for out in outputs)
+                ndims_params = [len(inp) for inp in inputs]
+
         if ndim_supp > 0:
             raise NotImplementedError(
                 "CustomDist with ndim_supp > 0 and without a `dist` function are not supported."
             )
 
         dist_params = [as_tensor_variable(param) for param in dist_params]
 
-        # Assume scalar ndims_params
-        if ndims_params is None:
-            ndims_params = [0] * len(dist_params)
-
         if logp is None:
             logp = default_not_implemented(class_name, "logp")
 
@@ -614,7 +649,7 @@ def rv_op(
         random: Optional[Callable],
         support_point: Optional[Callable],
         ndim_supp: int,
-        ndims_params: Optional[Sequence[int]],
+        ndims_params: Sequence[int],
         dtype: str,
         class_name: str,
         **kwargs,
@@ -702,7 +737,9 @@ def dist(
         logp: Optional[Callable] = None,
         logcdf: Optional[Callable] = None,
         support_point: Optional[Callable] = None,
-        ndim_supp: int = 0,
+        ndim_supp: Optional[int] = None,
+        ndims_params: Optional[Sequence[int]] = None,
+        signature: Optional[str] = None,
         dtype: str = "floatX",
         class_name: str = "CustomDist",
         **kwargs,
@@ -712,14 +749,24 @@ def dist(
         if logcdf is None:
             logcdf = default_not_implemented(class_name, "logcdf")
 
+        if signature is None:
+            if ndim_supp is None:
+                ndim_supp = 0
+            if ndims_params is None:
+                ndims_params = [0] * len(dist_params)
+            signature = safe_signature(
+                core_inputs=[pt.tensor(shape=(None,) * ndim_param) for ndim_param in ndims_params],
+                core_outputs=[pt.tensor(shape=(None,) * ndim_supp)],
+            )
+
         return super().dist(
             dist_params,
             class_name=class_name,
             logp=logp,
             logcdf=logcdf,
             dist=dist,
             support_point=support_point,
-            ndim_supp=ndim_supp,
+            signature=signature,
             **kwargs,
         )
 
@@ -732,7 +779,7 @@ def rv_op(
         logcdf: Optional[Callable],
         support_point: Optional[Callable],
         size=None,
-        ndim_supp: int,
+        signature: str,
         class_name: str,
     ):
         size = normalize_size_param(size)
@@ -745,6 +792,10 @@ def rv_op(
         dummy_params = [dummy_size_param, *dummy_dist_params]
         dummy_updates_dict = collect_default_updates(inputs=dummy_params, outputs=(dummy_rv,))
 
+        signature = cls._infer_final_signature(
+            signature, len(dummy_params), len(dummy_updates_dict)
+        )
+
         rv_type = type(
             class_name,
             (CustomSymbolicDistRV,),
@@ -802,7 +853,7 @@ def change_custom_symbolic_dist_size(op, rv, new_size, expand):
             new_rv_op = rv_type(
                 inputs=dummy_params,
                 outputs=[*dummy_updates_dict.values(), dummy_rv],
-                ndim_supp=ndim_supp,
+                signature=signature,
             )
             new_rv = new_rv_op(new_size, *dist_params)
 
@@ -811,10 +862,30 @@ def change_custom_symbolic_dist_size(op, rv, new_size, expand):
         rv_op = rv_type(
             inputs=dummy_params,
             outputs=[*dummy_updates_dict.values(), dummy_rv],
-            ndim_supp=ndim_supp,
+            signature=signature,
         )
         return rv_op(size, *dist_params)
 
+    @staticmethod
+    def _infer_final_signature(signature: str, n_inputs, n_updates) -> str:
+        """Add size and updates to user provided gufunc signature if they are missing."""
+        input_sig, output_sig = signature.split("->")
+        # Numpy parser does not accept (constant) functions without inputs like "->()"
+        # We work around as this makes sense for distributions like Flat that have no inputs
+        if input_sig.strip() == "":
+            inputs = ()
+            _, outputs = _parse_gufunc_signature("()" + signature)
+        else:
+            inputs, outputs = _parse_gufunc_signature(signature)
+        if len(inputs) == n_inputs - 1:
+            # Assume size is missing
+            input_sig = ("()," if input_sig else "()") + input_sig
+        if len(outputs) == 1:
+            # Assume updates are missing
+            output_sig = "()," * n_updates + output_sig
+        signature = "->".join((input_sig, output_sig))
+        return signature
+
 
 class CustomDist:
     """A helper class to create custom distributions
@@ -828,12 +899,12 @@ class CustomDist:
     when not provided by the user.
 
     Alternatively, a user can provide a `random` function that returns numerical
-    draws (e.g., via NumPy routines), and a `logp` function that must return an
-    Python graph that represents the logp graph when evaluated. This is used for
+    draws (e.g., via NumPy routines), and a `logp` function that must return a
+    PyTensor graph that represents the logp graph when evaluated. This is used for
     mcmc sampling.
 
     Additionally, a user can provide a `logcdf` and `support_point` functions that must return
-    an PyTensor graph that computes those quantities. These may be used by other PyMC
+    PyTensor graphs that computes those quantities. These may be used by other PyMC
     routines.
 
     Parameters
@@ -894,14 +965,18 @@ class CustomDist:
         distribution parameters, in the same order as they were supplied when the
         CustomDist was created. If ``None``, a default  ``support_point`` function will be
         assigned that will always return 0, or an array of zeros.
-    ndim_supp : int
-        The number of dimensions in the support of the distribution. Defaults to assuming
-        a scalar distribution, i.e. ``ndim_supp = 0``.
+    ndim_supp : Optional[int]
+        The number of dimensions in the support of the distribution.
+        Inferred from signature, if provided. Defaults to assuming
+        a scalar distribution, i.e. ``ndim_supp = 0``
     ndims_params : Optional[Sequence[int]]
         The list of number of dimensions in the support of each of the distribution's
-        parameters. If ``None``, it is assumed that all parameters are scalars, hence
-        the number of dimensions of their support will be 0. This is not needed if an
-        PyTensor dist function is provided.
+        parameters. Inferred from signature, if provided. Defaults to assuming
+        all parameters are scalars, i.e. ``ndims_params=[0, ...]``.
+    signature : Optional[str]
+        A numpy vectorize-like signature that indicates the number and core dimensionality
+        of the input parameters and sample outputs of the CustomDist.
+        When specified, `ndim_supp` and `ndims_params` are not needed. See examples below.
     dtype : str
         The dtype of the distribution. All draws and observations passed into the
         distribution will be cast onto this dtype. This is not needed if an PyTensor
@@ -939,6 +1014,7 @@ def logp(value: TensorVariable, mu: TensorVariable) -> TensorVariable:
 
     Provide a random function that return numerical draws. This allows one to use a
     CustomDist in prior and posterior predictive sampling.
+    A gufunc signature was also provided, which may be used by other routines.
 
     .. code-block:: python
 
@@ -965,6 +1041,7 @@ def random(
                 mu,
                 logp=logp,
                 random=random,
+                signature="()->()",
                 observed=np.random.randn(100, 3),
                 size=(100, 3),
             )
@@ -973,6 +1050,7 @@ def random(
     Provide a dist function that creates a PyTensor graph built from other
     PyMC distributions. PyMC can automatically infer that the logp of this
     variable corresponds to a shifted Exponential distribution.
+    A gufunc signature was also provided, which may be used by other routines.
 
     .. code-block:: python
 
@@ -994,6 +1072,7 @@ def dist(
                 lam,
                 shift,
                 dist=dist,
+                signature="(),()->()",
                 observed=[-1, -1, 0],
             )
 
@@ -1040,10 +1119,11 @@ def __new__(
         random: Optional[Callable] = None,
         logp: Optional[Callable] = None,
         logcdf: Optional[Callable] = None,
-        moment: Optional[Callable] = None,
         support_point: Optional[Callable] = None,
-        ndim_supp: int = 0,
+        # TODO: Deprecate ndim_supp / ndims_params in favor of signature?
+        ndim_supp: Optional[int] = None,
         ndims_params: Optional[Sequence[int]] = None,
+        signature: Optional[str] = None,
         dtype: str = "floatX",
         **kwargs,
     ):
@@ -1057,6 +1137,7 @@ def __new__(
             )
         dist_params = cls.parse_dist_params(dist_params)
         cls.check_valid_dist_random(dist, random, dist_params)
+        moment = kwargs.pop("moment", None)
         if moment is not None:
             warnings.warn(
                 "`moment` argument is deprecated. Use `support_point` instead.",
@@ -1073,6 +1154,8 @@ def __new__(
                 logcdf=logcdf,
                 support_point=support_point,
                 ndim_supp=ndim_supp,
+                ndims_params=ndims_params,
+                signature=signature,
                 **kwargs,
             )
         else:
@@ -1086,6 +1169,7 @@ def __new__(
                 support_point=support_point,
                 ndim_supp=ndim_supp,
                 ndims_params=ndims_params,
+                signature=signature,
                 dtype=dtype,
                 **kwargs,
             )
@@ -1099,8 +1183,9 @@ def dist(
         logp: Optional[Callable] = None,
         logcdf: Optional[Callable] = None,
         support_point: Optional[Callable] = None,
-        ndim_supp: int = 0,
+        ndim_supp: Optional[int] = None,
         ndims_params: Optional[Sequence[int]] = None,
+        signature: Optional[str] = None,
         dtype: str = "floatX",
         **kwargs,
     ):
@@ -1114,6 +1199,8 @@ def dist(
                 logcdf=logcdf,
                 support_point=support_point,
                 ndim_supp=ndim_supp,
+                ndims_params=ndims_params,
+                signature=signature,
                 **kwargs,
             )
         else:
@@ -1125,6 +1212,7 @@ def dist(
                 support_point=support_point,
                 ndim_supp=ndim_supp,
                 ndims_params=ndims_params,
+                signature=signature,
                 dtype=dtype,
                 **kwargs,
             )

pymc/distributions/mixture.py

@@ -296,10 +296,17 @@ def rv_op(cls, weights, *components, size=None):
         # Output mix_indexes rng update so that it can be updated in place
         mix_indexes_rng_next_ = mix_indexes_.owner.outputs[0]
 
+        s = ",".join(f"s{i}" for i in range(components[0].owner.op.ndim_supp))
+        if len(components) == 1:
+            comp_s = ",".join((*s, "w"))
+            signature = f"(),(w),({comp_s})->({s})"
+        else:
+            comps_s = ",".join(f"({s})" for _ in components)
+            signature = f"(),(w),{comps_s}->({s})"
         mix_op = MarginalMixtureRV(
             inputs=[mix_indexes_rng_, weights_, *components_],
             outputs=[mix_indexes_rng_next_, mix_out_],
-            ndim_supp=components[0].owner.op.ndim_supp,
+            signature=signature,
         )
 
         # Create the actual MarginalMixture variable