From d4e1098f475220d7ff3ea127d57b3eddfc721731 Mon Sep 17 00:00:00 2001
From: Alessandro Gentili <alessandro.gentili001@gmail.com>
Date: Sat, 28 Feb 2026 09:59:44 +0100
Subject: [PATCH] extending inv_as_solve to batched/Blockwise operations

---
 pytensor/tensor/rewriting/linalg.py   | 37 +++++++++++++--------------
 tests/tensor/rewriting/test_linalg.py | 29 +++++++++++++++++++++
 2 files changed, 47 insertions(+), 19 deletions(-)

diff --git a/pytensor/tensor/rewriting/linalg.py b/pytensor/tensor/rewriting/linalg.py
index 2c17020cd9..5bd5fa4c0e 100644
--- a/pytensor/tensor/rewriting/linalg.py
+++ b/pytensor/tensor/rewriting/linalg.py
@@ -132,29 +132,28 @@ def transinv_to_invtrans(fgraph, node):
 
 
 @register_stabilize
-@node_rewriter([Dot])
+@node_rewriter([Dot, _matmul])
 def inv_as_solve(fgraph, node):
     """
     This utilizes a boolean `symmetric` tag on the matrices.
     """
-    if isinstance(node.op, Dot):
-        l, r = node.inputs
-        if (
-            l.owner
-            and isinstance(l.owner.op, Blockwise)
-            and isinstance(l.owner.op.core_op, MatrixInverse)
-        ):
-            return [solve(l.owner.inputs[0], r)]
-        if (
-            r.owner
-            and isinstance(r.owner.op, Blockwise)
-            and isinstance(r.owner.op.core_op, MatrixInverse)
-        ):
-            x = r.owner.inputs[0]
-            if getattr(x.tag, "symmetric", None) is True:
-                return [solve(x, (l.mT)).mT]
-            else:
-                return [solve((x.mT), (l.mT)).mT]
+    l, r = node.inputs
+    if (
+        l.owner
+        and isinstance(l.owner.op, Blockwise)
+        and isinstance(l.owner.op.core_op, MatrixInverse)
+    ):
+        return [solve(l.owner.inputs[0], r)]
+    if (
+        r.owner
+        and isinstance(r.owner.op, Blockwise)
+        and isinstance(r.owner.op.core_op, MatrixInverse)
+    ):
+        x = r.owner.inputs[0]
+        if getattr(x.tag, "symmetric", None) is True:
+            return [solve(x, (l.mT)).mT]
+        else:
+            return [solve((x.mT), (l.mT)).mT]
 
 
 @register_stabilize
diff --git a/tests/tensor/rewriting/test_linalg.py b/tests/tensor/rewriting/test_linalg.py
index 9e8783e51a..c1f89ca3a1 100644
--- a/tests/tensor/rewriting/test_linalg.py
+++ b/tests/tensor/rewriting/test_linalg.py
@@ -219,6 +219,35 @@ def test_matrix_inverse_solve():
     )
 
 
+@pytest.mark.parametrize(
+    "batch_shape",
+    [(), (5,), (3, 5)],
+    ids=["no_batch", "single_batch", "multi_batch"],
+)
+def test_batched_matrix_inverse_solve(batch_shape):
+    """Test that inv_as_solve fires for batched (matmul) operations."""
+    n = 4
+    shape = (*batch_shape, n, n)
+    A = pt.tensor("A", shape=shape, dtype="float64")
+    b = pt.tensor("b", shape=shape, dtype="float64")
+
+    # inv(A) @ b  should be rewritten to solve(A, b)
+    out = matmul(pt.linalg.inv(A), b)
+    f = pytensor.function([A, b], out, mode="FAST_RUN")
+
+    # Graph check: should contain Solve, not MatrixInverse
+    nodes = f.maker.fgraph.apply_nodes
+    has_solve = any(
+        isinstance(getattr(node.op, "core_op", node.op), Solve) for node in nodes
+    )
+    has_inv = any(
+        isinstance(getattr(node.op, "core_op", node.op), MatrixInverse)
+        for node in nodes
+    )
+    assert has_solve, "Expected Solve in the rewritten graph"
+    assert not has_inv, "MatrixInverse should have been rewritten away"
+
+
 @pytest.mark.parametrize("tag", ("lower", "upper", None))
 @pytest.mark.parametrize("cholesky_form", ("lower", "upper"))
 @pytest.mark.parametrize("product", ("lower", "upper", None))