Do not invert Gamma rate and fix JAX implementation of Gamma and Pareto

pytensor/link/jax/dispatch/random.py

@@ -216,21 +216,20 @@ def sample_fn(rng, size, dtype, *parameters):
 
 @jax_sample_fn.register(aer.ParetoRV)
 @jax_sample_fn.register(aer.GammaRV)
-def jax_sample_fn_shape_rate(op):
-    """JAX implementation of random variables in the shape-rate family.
+def jax_sample_fn_shape_scale(op):
+    """JAX implementation of random variables in the shape-scale family.
 
     JAX only implements the standard version of random variables in the
-    shape-rate family. We thus need to rescale the results manually.
+    shape-scale family. We thus need to rescale the results manually.
 
     """
     name = op.name
     jax_op = getattr(jax.random, name)
 
-    def sample_fn(rng, size, dtype, *parameters):
+    def sample_fn(rng, size, dtype, shape, scale):
         rng_key = rng["jax_state"]
         rng_key, sampling_key = jax.random.split(rng_key, 2)
-        (shape, rate) = parameters
-        sample = jax_op(sampling_key, shape, size, dtype) / rate
+        sample = jax_op(sampling_key, shape, size, dtype) * scale
         rng["jax_state"] = rng_key
         return (rng, sample)
 

pytensor/tensor/random/basic.py

@@ -1,4 +1,5 @@
 import abc
+import warnings
 from typing import List, Optional, Union
 
 import numpy as np
@@ -419,7 +420,7 @@ def __call__(self, mean=0.0, sigma=1.0, size=None, **kwargs):
 lognormal = LogNormalRV()
 
 
-class GammaRV(ScipyRandomVariable):
+class GammaRV(RandomVariable):
     r"""A gamma continuous random variable.
 
     The probability density function for `gamma` in terms of the shape parameter
@@ -443,7 +444,7 @@ class GammaRV(ScipyRandomVariable):
     dtype = "floatX"
     _print_name = ("Gamma", "\\operatorname{Gamma}")
 
-    def __call__(self, shape, rate, size=None, **kwargs):
+    def __call__(self, shape, scale, size=None, **kwargs):
         r"""Draw samples from a gamma distribution.
 
         Signature
@@ -455,23 +456,35 @@ def __call__(self, shape, rate, size=None, **kwargs):
         ----------
         shape
             The shape :math:`\alpha` of the gamma distribution. Must be positive.
-        rate
-            The rate :math:`\beta` of the gamma distribution. Must be positive.
+        scale
+            The scale :math:`1/\beta` of the gamma distribution. Must be positive.
         size
             Sample shape. If the given size is, e.g. `(m, n, k)` then `m * n * k`
             independent, identically distributed random variables are
             returned. Default is `None` in which case a single random variable
             is returned.
 
         """
-        return super().__call__(shape, 1.0 / rate, size=size, **kwargs)
+        return super().__call__(shape, scale, size=size, **kwargs)
 
-    @classmethod
-    def rng_fn_scipy(cls, rng, shape, scale, size):
-        return stats.gamma.rvs(shape, scale=scale, size=size, random_state=rng)
 
+_gamma = GammaRV()
+
+
+def gamma(shape, rate=None, scale=None, **kwargs):
+    # TODO: Remove helper when rate is deprecated
+    if rate is not None and scale is not None:
+        raise ValueError("Cannot specify both rate and scale")
+    elif rate is None and scale is None:
+        raise ValueError("Must specify scale")
+    elif rate is not None:
+        warnings.warn(
+            "Gamma rate argument is deprecated and will stop working, use scale instead",
+            FutureWarning,
+        )
+        scale = 1.0 / rate
 
-gamma = GammaRV()
+    return _gamma(shape, scale, **kwargs)
 
 
 class ChiSquareRV(RandomVariable):

pytensor/tensor/random/rewriting/jax.py

@@ -15,9 +15,9 @@
     LogNormalRV,
     NegBinomialRV,
     WaldRV,
+    _gamma,
     beta,
     binomial,
-    gamma,
     normal,
     poisson,
     uniform,
@@ -92,29 +92,29 @@ def geometric_from_uniform(fgraph, node):
 @node_rewriter([NegBinomialRV])
 def negative_binomial_from_gamma_poisson(fgraph, node):
     rng, *other_inputs, n, p = node.inputs
-    next_rng, g = gamma.make_node(rng, *other_inputs, n, p / (1 - p)).outputs
+    next_rng, g = _gamma.make_node(rng, *other_inputs, n, (1 - p) / p).outputs
     next_rng, p = poisson.make_node(next_rng, *other_inputs, g).outputs
     return [next_rng, p]
 
 
 @node_rewriter([InvGammaRV])
 def inverse_gamma_from_gamma(fgraph, node):
     *other_inputs, shape, scale = node.inputs
-    next_rng, g = gamma.make_node(*other_inputs, shape, scale).outputs
+    next_rng, g = _gamma.make_node(*other_inputs, shape, 1 / scale).outputs
     return [next_rng, reciprocal(g)]
 
 
 @node_rewriter([ChiSquareRV])
 def chi_square_from_gamma(fgraph, node):
     *other_inputs, df = node.inputs
-    next_rng, g = gamma.make_node(*other_inputs, df / 2, 1 / 2).outputs
+    next_rng, g = _gamma.make_node(*other_inputs, df / 2, 2).outputs
     return [next_rng, g]
 
 
 @node_rewriter([GenGammaRV])
 def generalized_gamma_from_gamma(fgraph, node):
     *other_inputs, alpha, p, lambd = node.inputs
-    next_rng, g = gamma.make_node(*other_inputs, alpha / p, ones_like(lambd)).outputs
+    next_rng, g = _gamma.make_node(*other_inputs, alpha / p, ones_like(lambd)).outputs
     g = (g ** reciprocal(p)) * lambd
     return [next_rng, cast(g, dtype=node.default_output().dtype)]
 

tests/link/jax/test_random.py

@@ -4,7 +4,7 @@
 
 import pytensor
 import pytensor.tensor as at
-import pytensor.tensor.random as aer
+import pytensor.tensor.random.basic as aer
 from pytensor.compile.function import function
 from pytensor.compile.sharedvalue import SharedVariable, shared
 from pytensor.graph.basic import Constant
@@ -140,15 +140,15 @@ def test_random_updates_input_storage_order():
             lambda *args: (0, args[0]),
         ),
         (
-            aer.gamma,
+            aer._gamma,
             [
                 set_test_value(
                     at.dvector(),
                     np.array([1.0, 2.0], dtype=np.float64),
                 ),
                 set_test_value(
-                    at.dscalar(),
-                    np.array(1.0, dtype=np.float64),
+                    at.dvector(),
+                    np.array([0.5, 3.0], dtype=np.float64),
                 ),
             ],
             (2,),
@@ -235,11 +235,15 @@ def test_random_updates_input_storage_order():
                 set_test_value(
                     at.dvector(),
                     np.array([1.0, 2.0], dtype=np.float64),
-                )
+                ),
+                set_test_value(
+                    at.dvector(),
+                    np.array([2.0, 10.0], dtype=np.float64),
+                ),
             ],
             (2,),
             "pareto",
-            lambda *args: args,
+            lambda shape, scale: (shape, 0.0, scale),
         ),
         (
             aer.poisson,

tests/link/numba/test_random.py

@@ -92,6 +92,10 @@
                     at.dvector(),
                     np.array([1.0, 2.0], dtype=np.float64),
                 ),
+                set_test_value(
+                    at.dvector(),
+                    np.array([2.0, 10.0], dtype=np.float64),
+                ),
             ],
             at.as_tensor([3, 2]),
             marks=pytest.mark.xfail(reason="Not implemented"),
@@ -316,15 +320,15 @@ def test_aligned_RandomVariable(rv_op, dist_args, size):
             lambda *args: args,
         ),
         (
-            aer.gamma,
+            aer._gamma,
             [
                 set_test_value(
                     at.dvector(),
                     np.array([1.0, 2.0], dtype=np.float64),
                 ),
                 set_test_value(
-                    at.dscalar(),
-                    np.array(1.0, dtype=np.float64),
+                    at.dvector(),
+                    np.array([0.5, 3.0], dtype=np.float64),
                 ),
             ],
             (2,),

tests/tensor/random/test_basic.py

@@ -17,6 +17,7 @@
 from pytensor.graph.replace import clone_replace
 from pytensor.graph.rewriting.db import RewriteDatabaseQuery
 from pytensor.tensor.random.basic import (
+    _gamma,
     bernoulli,
     beta,
     betabinom,
@@ -351,20 +352,31 @@ def test_lognormal_samples(mean, sigma, size):
     ],
 )
 def test_gamma_samples(a, b, size):
-    gamma_test_fn = fixed_scipy_rvs("gamma")
-
-    def test_fn(shape, rate, **kwargs):
-        return gamma_test_fn(shape, scale=1.0 / rate, **kwargs)
-
     compare_sample_values(
-        gamma,
+        _gamma,
         a,
         b,
         size=size,
-        test_fn=test_fn,
     )
 
 
+def test_gamma_deprecation_wrapper_fn():
+    out = gamma(5.0, scale=0.5, size=(5,))
+    assert out.type.shape == (5,)
+    assert out.owner.inputs[-1].eval() == 0.5
+
+    with pytest.warns(FutureWarning, match="Gamma rate argument is deprecated"):
+        out = gamma([5.0, 10.0], 2.0, size=None)
+    assert out.type.shape == (2,)
+    assert out.owner.inputs[-1].eval() == 0.5
+
+    with pytest.raises(ValueError, match="Must specify scale"):
+        gamma(5.0)
+
+    with pytest.raises(ValueError, match="Cannot specify both rate and scale"):
+        gamma(5.0, rate=2.0, scale=0.5)
+
+
 @pytest.mark.parametrize(
     "df, size",
     [
@@ -470,18 +482,24 @@ def test_vonmises_samples(mu, kappa, size):
 
 
 @pytest.mark.parametrize(
-    "alpha, size",
+    "alpha, scale, size",
     [
-        (np.array(0.5, dtype=config.floatX), None),
-        (np.array(0.5, dtype=config.floatX), []),
+        (np.array(0.5, dtype=config.floatX), np.array(3.0, dtype=config.floatX), None),
+        (np.array(0.5, dtype=config.floatX), np.array(5.0, dtype=config.floatX), []),
         (
             np.full((1, 2), 0.5, dtype=config.floatX),
+            np.array([0.5, 1.0], dtype=config.floatX),
             None,
         ),
     ],
 )
-def test_pareto_samples(alpha, size):
-    compare_sample_values(pareto, alpha, size=size, test_fn=fixed_scipy_rvs("pareto"))
+def test_pareto_samples(alpha, scale, size):
+    pareto_test_fn = fixed_scipy_rvs("pareto")
+
+    def test_fn(shape, scale, **kwargs):
+        return pareto_test_fn(shape, scale=scale, **kwargs)
+
+    compare_sample_values(pareto, alpha, scale, size=size, test_fn=test_fn)
 
 
 def mvnormal_test_fn(mean=None, cov=None, size=None, random_state=None):