Initial project scaffold

reference/torch_matmul.py

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+from __future__ import annotations
+
+import torch
+
+
+def torch_matmul(a: torch.Tensor, b: torch.Tensor) -> torch.Tensor:
+    """Reference matrix multiplication with simple shape validation."""
+    if a.ndim != 2 or b.ndim != 2:
+        raise ValueError("torch_matmul expects two 2D tensors")
+    if a.shape[1] != b.shape[0]:
+        raise ValueError(f"incompatible shapes: {a.shape} and {b.shape}")
+    return a @ b
+