PennyLaneAI / PennyLaneAI/catalyst

mcm_method='one-shot' is not supported with a dynamic number of shots

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bug frontend
Dominant language
Python
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Forks
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Avg merge
2d 15h
Merged PRs (30d)
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Description

Possibly related to a similar issue with dynamic shapes in #1949, the dynamic one-shot transform does not work when the number of shots is a tracer value. The underlying issue is the vmap transform not being able to handle a dynamic batch size.

import pennylane as qml

@qml.qjit
def main(shots: int):

    @qml.qnode(qml.device("lightning.qubit", wires=1), mcm_method="one-shot")
    def f():
        qml.H(0)
        return qml.sample()

    return qml.set_shots(shots)(f)()

main(10)
  File "catalyst/frontend/catalyst/api_extensions/function_maps.py", line 368, in _get_batch_size
    if not batch_size:

jax.errors.TracerBoolConversionError: Attempted boolean conversion of traced array with shape int64[].

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Research direction

Start at catalyst/frontend/catalyst/api_extensions/function_maps.py, especially _get_batch_size, and reproduce the shown qjit example with main(10). Trace how the dynamic shots value reaches the vmap transform, then verify that the example runs without the reported TracerBoolConversionError.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
quantum-computing
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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