docs: add differentiability warning for Warp with mode='nearest' #8629
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WalkthroughThis PR adds an informational note to the Warp class constructor docstring in Estimated code review effort🎯 1 (Trivial) | ⏱️ ~2 minutes
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56-61: Fix minor formatting inconsistencies in the documentation note.The content is accurate and addresses the issue well, but two formatting tweaks are needed for consistency with the existing docstring style:
- Line 56: Remove the space after
=inmode=(should bemode="nearest"notmode= "nearest")- Line 58: Use backticks for code literals (
"bilinear","trilinear") instead of straight quotes, consistent with the rest of the docstringApply this diff to fix the formatting:
- Note that using mode= ``"nearest"`` makes the warping operation effectively non-differentiable: + Note that using mode=``"nearest"`` makes the warping operation effectively non-differentiable: gradients are zero almost everywhere, which can block gradient flow during training. - For learning-based registration, use "bilinear" (2D) or "trilinear" (3D) interpolation instead. + For learning-based registration, use ``"bilinear"`` (2D) or ``"trilinear"`` (3D) interpolation instead.
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Files:
monai/networks/blocks/warp.py
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Fixes #8540 .
Description
This PR updates the docstring of monai.networks.blocks.Warp to clarify that mode='nearest' results in zero gradients almost everywhere, effectively blocking gradient flow in registration training.
Changes:
Added a note to the Warp docstring about the gradient behavior of mode='nearest'.
Added a reference to the semi-supervised registration tutorial:
https://github.com/Project-MONAI/tutorials/blob/main/3d_registration/learn2reg_oasis_unpaired_brain_mr.ipynb
Next Steps (future PR):
Extend VoxelMorph.forward to handle optional label and keypoint arguments for consistent warping behavior.
Types of changes
./runtests.sh -f -u --net --coverage../runtests.sh --quick --unittests --disttests.make htmlcommand in thedocs/folder.