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Fix PyTorch random.multinomial sequence inputs #2225

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FlorianPfaff merged 2 commits into from
May 24, 2026
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Fix PyTorch random.multinomial sequence inputs #2225

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ff34b36
Fix PyTorch multinomial probability input coercion
FlorianPfaff May 24, 2026
43a6453
Add multinomial probability sequence regression test
FlorianPfaff May 24, 2026
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2 changes: 2 additions & 0 deletions src/pyrecest/_backend/pytorch/random.py
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Original file line number Diff line number Diff line change
Expand Up @@ -120,6 +120,8 @@ def rand(size=None, dtype=None):


def multinomial(n, pvals):
device = pvals.device if _torch.is_tensor(pvals) else None
pvals = _torch.as_tensor(pvals, dtype=_torch.float32, device=device)
pvals = pvals / pvals.sum()
return _torch.multinomial(pvals, n, replacement=True).bincount(minlength=len(pvals))

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6 changes: 6 additions & 0 deletions tests/test_backend_random.py
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Expand Up @@ -70,6 +70,12 @@ def test_choice_samples_matrix_values_along_requested_axis(self):
self.assertTrue(set(sample_np[0].tolist()).issubset({0, 1, 2}))
self.assertTrue(set(sample_np[1].tolist()).issubset({3, 4, 5}))

def test_multinomial_accepts_python_probability_sequence(self):
sample = random.multinomial(12, [0.25, 0.75])

self.assertEqual(sample.shape, (2,))
self.assertEqual(int(pyrecest.backend.sum(sample)), 12)

@unittest.skipIf(
pyrecest.backend.__backend_name__ != "jax", "JAX-specific RNG state contract"
)
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