Implement vectorize_node for Softmax and Argmax Ops

Also refactors shared logic for other batch axed Ops

Author: ricardoV94

pytensor/tensor/basic.py

@@ -43,7 +43,12 @@
     get_vector_length,
 )
 from pytensor.tensor.blockwise import Blockwise
-from pytensor.tensor.elemwise import DimShuffle, Elemwise, scalar_elemwise
+from pytensor.tensor.elemwise import (
+    DimShuffle,
+    Elemwise,
+    get_normalized_batch_axes,
+    scalar_elemwise,
+)
 from pytensor.tensor.exceptions import NotScalarConstantError
 from pytensor.tensor.shape import (
     Shape,
@@ -3614,13 +3619,18 @@ def diagonal(a, offset=0, axis1=0, axis2=1):
 
 
 @_vectorize_node.register(ExtractDiag)
-def vectorize_extract_diag(op: ExtractDiag, node, batched_x):
-    batched_ndims = batched_x.type.ndim - node.inputs[0].type.ndim
+def vectorize_extract_diag(op: ExtractDiag, node, batch_x):
+    core_ndim = node.inputs[0].type.ndim
+    batch_ndim = batch_x.type.ndim - core_ndim
+    batch_axis1, batch_axis2 = get_normalized_batch_axes(
+        (op.axis1, op.axis2), core_ndim, batch_ndim
+    )
+
     return diagonal(
-        batched_x,
+        batch_x,
         offset=op.offset,
-        axis1=op.axis1 + batched_ndims,
-        axis2=op.axis2 + batched_ndims,
+        axis1=batch_axis1,
+        axis2=batch_axis2,
     ).owner
 
 

pytensor/tensor/elemwise.py

@@ -1,6 +1,8 @@
 from copy import copy
+from typing import Union
 
 import numpy as np
+from numpy.core.numeric import normalize_axis_tuple
 
 import pytensor.tensor.basic
 from pytensor.configdefaults import config
@@ -1399,7 +1401,7 @@ def make_node(self, input):
         # scalar inputs are treated as 1D regarding axis in this `Op`
         if axis is not None:
             try:
-                axis = np.core.numeric.normalize_axis_tuple(axis, ndim=max(1, inp_dims))
+                axis = normalize_axis_tuple(axis, ndim=max(1, inp_dims))
             except np.AxisError:
                 raise np.AxisError(axis, ndim=inp_dims)
 
@@ -1757,18 +1759,36 @@ def vectorize_dimshuffle(op: DimShuffle, node: Apply, x: TensorVariable) -> Appl
     return DimShuffle(input_broadcastable, new_order).make_node(x)
 
 
-@_vectorize_node.register(CAReduce)
-def vectorize_careduce(op: CAReduce, node: Apply, x: TensorVariable) -> Apply:
-    batched_ndims = x.type.ndim - node.inputs[0].type.ndim
-    if not batched_ndims:
-        return node.op.make_node(x)
-    axes = op.axis
-    # e.g., sum(matrix, axis=None) -> sum(tensor4, axis=(2, 3))
-    # e.g., sum(matrix, axis=0) -> sum(tensor4, axis=(2,))
-    if axes is None:
-        axes = list(range(node.inputs[0].type.ndim))
+def get_normalized_batch_axes(
+    core_axes: Union[None, int, tuple[int, ...]],
+    core_ndim: int,
+    batch_ndim: int,
+) -> tuple[int, ...]:
+    """Compute batch axes for a batched operation, from the core input ndim and axes.
+
+    e.g., sum(matrix, axis=None) -> sum(tensor4, axis=(2, 3))
+    batch_axes(None, 2, 4) -> (2, 3)
+
+    e.g., sum(matrix, axis=0) -> sum(tensor4, axis=(2,))
+    batch_axes(0, 2, 4) -> (2,)
+
+    e.g., sum(tensor3, axis=(0, -1)) -> sum(tensor4, axis=(1, 3))
+    batch_axes((0, -1), 3, 4) -> (1, 3)
+    """
+    if core_axes is None:
+        core_axes = tuple(range(core_ndim))
     else:
-        axes = list(axes)
-    new_axes = [axis + batched_ndims for axis in axes]
-    new_op = op.clone(axis=new_axes)
-    return new_op.make_node(x)
+        core_axes = normalize_axis_tuple(core_axes, core_ndim)
+    return tuple(core_axis + batch_ndim for core_axis in core_axes)
+
+
+@_vectorize_node.register(CAReduce)
+def vectorize_careduce(op: CAReduce, node: Apply, batch_x: TensorVariable) -> Apply:
+    core_ndim = node.inputs[0].type.ndim
+    batch_ndim = batch_x.type.ndim - core_ndim
+
+    if not batch_ndim:
+        return node.op.make_node(batch_x)
+
+    batch_axes = get_normalized_batch_axes(op.axis, core_ndim, batch_ndim)
+    return op.clone(axis=batch_axes).make_node(batch_x)

pytensor/tensor/math.py

@@ -27,7 +27,13 @@
     switch,
 )
 from pytensor.tensor.blockwise import Blockwise, vectorize_node_fallback
-from pytensor.tensor.elemwise import CAReduce, DimShuffle, Elemwise, scalar_elemwise
+from pytensor.tensor.elemwise import (
+    CAReduce,
+    DimShuffle,
+    Elemwise,
+    get_normalized_batch_axes,
+    scalar_elemwise,
+)
 from pytensor.tensor.shape import shape, specify_broadcastable
 from pytensor.tensor.type import (
     DenseTensorType,
@@ -134,7 +140,7 @@ class MaxAndArgmax(COp):
     _f16_ok = True
 
     def __init__(self, axis):
-        assert isinstance(axis, list)
+        assert isinstance(axis, (tuple, list))
         self.axis = tuple(axis)
 
     def get_params(self, node):
@@ -465,6 +471,19 @@ def grad(self, inp, grads):
         return [x.zeros_like()]
 
 
+@_vectorize_node.register(Argmax)
+@_vectorize_node.register(MaxAndArgmax)
+def vectorize_argmax_node(op, node, batch_x):
+    core_ndim = node.inputs[0].type.ndim
+    batch_ndim = batch_x.type.ndim - core_ndim
+
+    if not batch_ndim:
+        return node.op.make_node(batch_x)
+
+    batch_axes = get_normalized_batch_axes(op.axis, core_ndim, batch_ndim)
+    return type(op)(axis=batch_axes).make_node(batch_x)
+
+
 def makeKeepDims(x, y, axis):
     """
     Reintroduces in y with length one the axes of x which have been left out

pytensor/tensor/shape.py

@@ -18,6 +18,7 @@
 from pytensor.tensor import _get_vector_length, as_tensor_variable
 from pytensor.tensor import basic as ptb
 from pytensor.tensor import get_vector_length
+from pytensor.tensor.elemwise import get_normalized_batch_axes
 from pytensor.tensor.exceptions import NotScalarConstantError
 from pytensor.tensor.type import DenseTensorType, TensorType, int_dtypes, tensor
 from pytensor.tensor.type_other import NoneConst
@@ -1103,8 +1104,10 @@ def unbroadcast(x, *axes):
 
 
 @_vectorize_node.register(Unbroadcast)
-def _vectorize_unbroadcast(op: Unbroadcast, node: Apply, x: TensorVariable) -> Apply:
-    batched_ndims = x.type.ndim - node.inputs[0].type.ndim
-    old_axes = op.axes
-    new_axes = (old_axis + batched_ndims for old_axis in old_axes)
-    return cast(Apply, unbroadcast(x, *new_axes).owner)
+def _vectorize_unbroadcast(
+    op: Unbroadcast, node: Apply, batch_x: TensorVariable
+) -> Apply:
+    core_ndim = node.inputs[0].type.ndim
+    batch_ndim = batch_x.type.ndim - core_ndim
+    batch_axes = get_normalized_batch_axes(op.axes, core_ndim, batch_ndim)
+    return cast(Apply, unbroadcast(batch_x, *batch_axes).owner)

pytensor/tensor/special.py

@@ -4,8 +4,10 @@
 import scipy
 
 from pytensor.graph.basic import Apply
+from pytensor.graph.replace import _vectorize_node
 from pytensor.link.c.op import COp
 from pytensor.tensor.basic import as_tensor_variable
+from pytensor.tensor.elemwise import get_normalized_batch_axes
 from pytensor.tensor.math import gamma, gammaln, neg, sum
 
 
@@ -736,6 +738,32 @@ def log_softmax(c, axis=None):
     return LogSoftmax(axis=axis)(c)
 
 
+@_vectorize_node.register(Softmax)
+@_vectorize_node.register(LogSoftmax)
+def vectorize_softmax_node(op, node, batched_x):
+    """
+    Vectorize Softmax and LogSoftmax nodes.
+
+    """
+    core_ndim = node.inputs[0].type.ndim
+    batch_ndim = batched_x.type.ndim - core_ndim
+
+    if not batch_ndim:
+        return op.make_node(batched_x)
+
+    batch_axes = get_normalized_batch_axes(op.axis, core_ndim, batch_ndim)
+
+    if len(batch_axes) > 1:
+        from pytensor.tensor.blockwise import vectorize_node_fallback
+
+        # The softmax Ops only allow a specific axis (integer) or all axis (None).
+        # If the vectorized operation requires more than one axis we have to default to a Blockwise
+        return vectorize_node_fallback(op, node, batched_x)
+
+    [batch_axis] = batch_axes
+    return type(op)(axis=batch_axis).make_node(batched_x)
+
+
 def poch(z, m):
     """
     Pochhammer symbol (rising factorial) function.

tests/tensor/test_math.py

@@ -20,6 +20,7 @@
 from pytensor.gradient import NullTypeGradError, grad, numeric_grad
 from pytensor.graph.basic import Variable, applys_between
 from pytensor.graph.fg import FunctionGraph
+from pytensor.graph.replace import vectorize_node
 from pytensor.link.c.basic import DualLinker
 from pytensor.misc.safe_asarray import _asarray
 from pytensor.printing import pprint
@@ -1010,6 +1011,35 @@ def test_numpy_input(self):
         assert max_pt.eval() == 3
         assert argmax_pt.eval() == 2
 
+    @pytest.mark.parametrize(
+        "core_axis, batch_axis",
+        [
+            (None, (1, 2, 3, 4)),
+            (0, (1,)),
+            ((1, -1), (2, 4)),
+        ],
+    )
+    def test_vectorize(self, core_axis, batch_axis):
+        x = tensor(shape=(5, 5, 5, 5))
+        batch_x = tensor(shape=(3, 5, 5, 5, 5))
+
+        # Test MaxAndArgmax
+        max_x, argmax_x = max_and_argmax(x, axis=core_axis)
+        node = max_x.owner
+        assert isinstance(node.op, MaxAndArgmax)
+
+        new_node = vectorize_node(node, batch_x)
+        assert isinstance(new_node.op, MaxAndArgmax)
+        assert new_node.op.axis == batch_axis
+
+        # Test Argmax
+        # Argmax is not user-facing, so we have to create it manually
+        node = Argmax(axis=node.op.axis).make_node(x)
+
+        new_node = vectorize_node(node, batch_x)
+        assert isinstance(new_node.op, Argmax)
+        assert new_node.op.axis == batch_axis
+
 
 class TestArgminArgmax:
     def setup_method(self):

tests/tensor/test_special.py

@@ -8,6 +8,8 @@
 
 from pytensor.compile.function import function
 from pytensor.configdefaults import config
+from pytensor.graph.replace import vectorize_node
+from pytensor.tensor.blockwise import Blockwise
 from pytensor.tensor.special import (
     LogSoftmax,
     Softmax,
@@ -19,7 +21,7 @@
     poch,
     softmax,
 )
-from pytensor.tensor.type import matrix, tensor3, tensor4, vector, vectors
+from pytensor.tensor.type import matrix, tensor, tensor3, tensor4, vector, vectors
 from tests import unittest_tools as utt
 from tests.tensor.utils import random_ranged
 
@@ -150,6 +152,34 @@ def test_valid_axis(self):
             SoftmaxGrad(-4)(*x)
 
 
+@pytest.mark.parametrize(
+    "core_axis, batch_axis",
+    [
+        (None, (1, 2, 3, 4)),
+        (0, (1,)),
+    ],
+)
+@pytest.mark.parametrize(
+    "op, constructor", [(Softmax, softmax), (LogSoftmax, log_softmax)]
+)
+def test_vectorize_softmax(op, constructor, core_axis, batch_axis):
+    x = tensor(shape=(5, 5, 5, 5))
+    batch_x = tensor(shape=(3, 5, 5, 5, 5))
+
+    node = constructor(x, axis=core_axis).owner
+    assert isinstance(node.op, op)
+
+    new_node = vectorize_node(node, batch_x)
+    if len(batch_axis) == 1:
+        assert isinstance(new_node.op, op)
+        assert (new_node.op.axis,) == batch_axis
+    else:
+        assert isinstance(new_node.op, Blockwise) and isinstance(
+            new_node.op.core_op, op
+        )
+        assert new_node.op.core_op.axis == core_axis
+
+
 def test_poch():
     _z, _m = vectors("z", "m")
     actual_fn = function([_z, _m], poch(_z, _m))