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Fix ldexp grad for negative exponents #91

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Fix ldexp grad for negative exponents #91

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15 changes: 15 additions & 0 deletions test/test_binary_ufuncs.py
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Original file line number Diff line number Diff line change
Expand Up @@ -227,6 +227,21 @@ def test_lerp_lowp_cpu(self, dtype):
expected = torch.lerp(xref, yref, wref).to(dtype)
self.assertEqual(actual, expected, atol=0.0, rtol=0.0)

def test_ldexp_backward_negative_exponent(self):
mantissa = torch.tensor([1.0], requires_grad=True)
exponent = torch.tensor([-1], dtype=torch.int32)

torch.ldexp(mantissa, exponent).sum().backward()

self.assertEqual(mantissa.grad, torch.tensor([0.5]))

with fwAD.dual_level():
mantissa_dual = fwAD.make_dual(torch.tensor([1.0]), torch.tensor([1.0]))
result = torch.ldexp(mantissa_dual, exponent)
_, result_tangent = fwAD.unpack_dual(result)

self.assertEqual(result_tangent, torch.tensor([0.5]))


class TestBinaryUfuncsDevice(TestCase):
# Generic tests for elementwise binary (AKA binary universal (u) functions (funcs))
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4 changes: 2 additions & 2 deletions tools/autograd/derivatives.yaml
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Expand Up @@ -926,9 +926,9 @@
values: gather_with_keepdimed_indices(self_t, dim, indices, keepdim)

- name: ldexp.Tensor(Tensor self, Tensor other) -> Tensor
self: grad * at::pow(2, other).conj()
self: grad * at::pow(2.0, other).conj()
other: grad * result.conj() * M_LN2
result: self_t * at::pow(2, other_p) + other_t * result * M_LN2
result: self_t * at::pow(2.0, other_p) + other_t * result * M_LN2

- name: le_.Scalar(Tensor(a!) self, Scalar other) -> Tensor(a!)
self: zeros_like(self)
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