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Fix complex VJPs for log and exp #3605

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Fix complex VJPs for log and exp #3605

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12 changes: 10 additions & 2 deletions mlx/primitives.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1992,7 +1992,7 @@ std::vector<array> Exp::vjp(
const std::vector<array>& cotangents,
const std::vector<int>& argnums,
const std::vector<array>& outputs) {
return {multiply(cotangents[0], outputs[0], stream())};
return {multiply(cotangents[0], conjugate(outputs[0], stream()), stream())};
}

std::vector<array> Exp::jvp(
Expand Down Expand Up @@ -2713,7 +2713,15 @@ std::vector<array> Log::vjp(
const std::vector<array>& cotangents,
const std::vector<int>& argnums,
const std::vector<array>&) {
return jvp(primals, cotangents, argnums);
// return jvp(primals, cotangents, argnums);
assert(primals.size() == 1);
assert(argnums.size() == 1);
auto out = divide(cotangents[0], conjugate(primals[0], stream()), stream());
if (base_ != Base::e) {
auto scale = 1 / std::log(base_ == Base::ten ? 10.0f : 2.0f);
out = multiply(array(scale, out.dtype()), out, stream());
}
return {out};
}

std::vector<array> Log::jvp(
Expand Down
39 changes: 39 additions & 0 deletions python/tests/test_autograd.py
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Original file line number Diff line number Diff line change
Expand Up @@ -987,6 +987,45 @@ def prod(x):

self.assertTrue(mx.array_equal(mx.stack(vjps_multiply), vjps[0]))

def test_complex_exp_vjp(self):
primal = mx.random.normal((3, 4, 5), dtype=mx.complex64)
cotangent = mx.random.normal(
(
3,
4,
5,
),
dtype=mx.complex64,
)

_, vjps = mx.vjp(mx.exp, [primal], [cotangent])

expected = cotangent * mx.conj(mx.exp(primal))

# Check against hand-computed vjps
self.assertTrue(mx.allclose(vjps[0], expected))

def test_complex_log_vjp(self):
primal = mx.random.normal((3, 4, 5), dtype=mx.complex64)
cotangent = mx.random.normal(
(
3,
4,
5,
),
dtype=mx.complex64,
)

# guard against values too close to the origin
primal = mx.where(abs(primal) < 1e-3, 1e-3, primal)

_, vjps = mx.vjp(mx.log, [primal], [cotangent])

expected = cotangent * mx.conj(1 / primal)

# Check against hand-computed vjps
self.assertTrue(mx.allclose(vjps[0], expected))


if __name__ == "__main__":
mlx_tests.MLXTestRunner()