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pytorch3d_stub/pytorch3d/transforms/__init__.py

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+"""Minimal pytorch3d.transforms stub – quaternion operations only."""
+import torch
+
+def quaternion_multiply(q1: torch.Tensor, q2: torch.Tensor) -> torch.Tensor:
+    """Hamilton product of two quaternions (w, x, y, z)."""
+    w1, x1, y1, z1 = q1.unbind(-1)
+    w2, x2, y2, z2 = q2.unbind(-1)
+    return torch.stack([
+        w1*w2 - x1*x2 - y1*y2 - z1*z2,
+        w1*x2 + x1*w2 + y1*z2 - z1*y2,
+        w1*y2 - x1*z2 + y1*w2 + z1*x2,
+        w1*z2 + x1*y2 - y1*x2 + z1*w2,
+    ], dim=-1)
+
+def quaternion_invert(q: torch.Tensor) -> torch.Tensor:
+    """Invert a quaternion (w, x, y, z) -> (w, -x, -y, -z) / ||q||^2."""
+    scaling = torch.tensor([1, -1, -1, -1], device=q.device, dtype=q.dtype)
+    return q * scaling / (q * q).sum(dim=-1, keepdim=True).clamp(min=1e-10)