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Allow torch.arange() to return empty tensor when bounds are inconsistent with step sign#182133

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senekis316:fix/arange-empty-on-inconsistent-step
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Allow torch.arange() to return empty tensor when bounds are inconsistent with step sign#182133
senekis316 wants to merge 1 commit intopytorch:mainfrom
senekis316:fix/arange-empty-on-inconsistent-step

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@senekis316 senekis316 commented May 1, 2026

Fixes #70915

Per the Array API Standard, torch.arange(start, stop, step) should return
an empty tensor when stop-start and step have opposite signs, rather than
raising a RuntimeError. This aligns with NumPy's behavior.

Before:

torch.arange(1, 0)      # RuntimeError: upper bound and lower bound inconsistent with step sign
torch.arange(0, 1, -1)  # RuntimeError

**After:**
torch.arange(1, 0)      # tensor([], dtype=torch.int64)
torch.arange(0, 1, -1)  # tensor([], dtype=torch.int64)

**Changes:**
aten/src/ATen/native/RangeUtils.h: remove inconsistent-bounds check from arange_check_bounds; clamp size_d to 0 in compute_arange_size
torch/_refs/__init__.py: remove corresponding Python-layer check; clamp length to 0
torch/testing/_internal/common_methods_invocations.py: remove now-valid inputs from error_inputs_arange

@senekis316
Allow torch.arange() to return empty tensor when bounds are inconsist…
a896528 
…ent with step sign

Per the Array API Standard, torch.arange(start, stop, step) should return
an empty tensor when stop-start and step have opposite signs, rather than
raising a RuntimeError. This aligns with NumPy behavior.

- Remove the inconsistent-bounds TORCH_CHECK from arange_check_bounds (RangeUtils.h)
- Clamp computed size to 0 in compute_arange_size (RangeUtils.h)
- Remove the corresponding check in torch/_refs/__init__.py
- Update error_inputs_arange to remove now-valid inputs

Fixes pytorch#70915
@senekis316 senekis316 requested a review from mruberry as a code owner May 1, 2026 16:29
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pytorch-bot Bot commented May 1, 2026

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/182133

Note: Links to docs will display an error until the docs builds have been completed.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

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pytorch-bot Bot commented May 1, 2026

This PR needs a release notes: label

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@drisspg drisspg added the triaged This issue has been looked at a team member, and triaged and prioritized into an appropriate module label May 5, 2026
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arange should return empty array if bounds are inconsistent with step sign

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