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Remove complex warning from operator matrices #1802

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merged 11 commits into from
Oct 27, 2021
Merged

Remove complex warning from operator matrices #1802

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0ef30e7
Update operator matrices to remove complex casting warning
josh146 Oct 25, 2021
da3cdef
more operators
josh146 Oct 25, 2021
60d2544
more operators
josh146 Oct 25, 2021
7e4ace0
Update tests/ops/qubit/test_hamiltonian.py
josh146 Oct 25, 2021
f4508b3
Merge branch 'master' into remove-complex-warning
josh146 Oct 25, 2021
ce33ada
Merge branch 'master' into remove-complex-warning
josh146 Oct 25, 2021
befe446
Merge branch 'master' into remove-complex-warning
josh146 Oct 26, 2021
ee75d10
Merge branch 'master' into remove-complex-warning
josh146 Oct 26, 2021
d50d01f
Fix autograd warning in orbital rotation.
glassnotes Oct 26, 2021
11c0319
Update variable dtype in torch test to remove warning.
glassnotes Oct 26, 2021
d5e5bb2
Merge branch 'master' into remove-complex-warning
josh146 Oct 26, 2021
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43 changes: 23 additions & 20 deletions pennylane/ops/qubit/qchem_ops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -613,30 +613,33 @@ def _matrix(cls, *params):
# Additionally, there was a typo in the sign of a matrix element "s" at [2, 8], which is fixed here.

phi = params[0]
interface = qml.math.get_interface(phi)
c = qml.math.cos(phi / 2)
s = qml.math.sin(phi / 2)
z = qml.math.zeros([16], like=interface)

matrix = [
[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, c, 0, 0, -s, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, c, 0, 0, 0, 0, 0, -s, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, c ** 2, 0, 0, -c * s, 0, 0, -c * s, 0, 0, s ** 2, 0, 0, 0],
[0, s, 0, 0, c, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, c * s, 0, 0, c ** 2, 0, 0, -(s ** 2), 0, 0, -c * s, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, c, 0, 0, 0, 0, 0, -s, 0, 0],
[0, 0, s, 0, 0, 0, 0, 0, c, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, c * s, 0, 0, -(s ** 2), 0, 0, c ** 2, 0, 0, -c * s, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, c, 0, 0, -s, 0],
[0, 0, 0, s ** 2, 0, 0, c * s, 0, 0, c * s, 0, 0, c ** 2, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, s, 0, 0, 0, 0, 0, c, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, s, 0, 0, c, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
]
diag = qml.math.diag([1, c, c, c ** 2, c, 1, c ** 2, c, c, c ** 2, 1, c, c ** 2, c, c, 1])

# first stack each row and then stack all the rows
U = qml.math.stack([qml.math.stack(row) for row in matrix], axis=0)
U = diag + qml.math.stack(
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wait why does this fix it 🤯 what makes the diagonal part different???????????

This PR has made me so confused

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@josh146 josh146 Oct 26, 2021 •
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at some point in the future other devs are going to look at this and just be like why is the matrix coded like this hahahaha

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I know, I'm just totally baffled! It's the exact same matrix! We can always leave a humorous warning for the next dev who looks at it.

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... which, realistically, is going to be us and @mariaschuld while doing the operator refactor.

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@josh146 Hahaha, having a laugh reading through this, and finding myself in this statement:

at some point in the future other devs are going to look at this and just be like why is the matrix coded like this hahahaha

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In retrospect we should have added comments to the code, linking back to this PR for context to future developers 😆

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wait @dwierichs how did you find this PR

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I was wondering the same thing! 😂

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I am going to implement batching for parametrized operations and therefore need to modify this code :D
The version I'm currently going with is

@staticmethod
def compute_matrix(theta):
    c = qml.math.cos(theta / 2)
    s = qml.math.sin(theta / 2)
    if qml.math.get_interface(theta)=="tensorflow":
        c = qml.math.cast_like(c, 1j)
        s = qml.math.cast_like(s, 1j)
    
    mat = qml.math.stack([qml.math.stack([c, s]), qml.math.stack([s, c])])
    return mat * qml.math.array([[1+0j, -1j], [-1j, 1+0j]], like=mat)

which is batch-compatible (i.e. theta being non-scalar) and also is 20% or so faster in the scalar case :)

[
z,
qml.math.stack([0, 0, 0, 0, -s, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]),
qml.math.stack([0, 0, 0, 0, 0, 0, 0, 0, -s, 0, 0, 0, 0, 0, 0, 0]),
qml.math.stack([0, 0, 0, 0, 0, 0, -c * s, 0, 0, -c * s, 0, 0, s * s, 0, 0, 0]),
qml.math.stack([0, s, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]),
z,
qml.math.stack([0, 0, 0, c * s, 0, 0, 0, 0, 0, -s * s, 0, 0, -c * s, 0, 0, 0]),
qml.math.stack([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -s, 0, 0]),
qml.math.stack([0, 0, s, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]),
qml.math.stack([0, 0, 0, c * s, 0, 0, -s * s, 0, 0, 0, 0, 0, -c * s, 0, 0, 0]),
z,
qml.math.stack([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -s, 0]),
qml.math.stack([0, 0, 0, s * s, 0, 0, c * s, 0, 0, c * s, 0, 0, 0, 0, 0, 0]),
qml.math.stack([0, 0, 0, 0, 0, 0, 0, s, 0, 0, 0, 0, 0, 0, 0, 0]),
qml.math.stack([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, s, 0, 0, 0, 0]),
z,
]
)

return U

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