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circuit.insert_at_frontier crashes when inserting GlobalPhaseOperation #4225

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tanujkhattar opened this issue Jun 17, 2021 · 1 comment · Fixed by #4224
Closed

circuit.insert_at_frontier crashes when inserting GlobalPhaseOperation #4225

tanujkhattar opened this issue Jun 17, 2021 · 1 comment · Fixed by #4224
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area/circuits complexity/low introduces/modifies 1-2 concepts, should take 1-2 days max for an advanced contributor good first issue This issue can be resolved by someone who is not familiar with the codebase. A good starting issue. kind/bug-report Something doesn't seem to work. triage/accepted there is consensus amongst maintainers that this is a real bug or a reasonable feature to add

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@tanujkhattar
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Description of the issue
circuit.insert_at_frontier fails when trying to insert GlobalPhaseOperation because the operation does not have any qubits. As a result, PointOptimizer also fails when the new_operations contain a GlobalPhaseOperation.

How to reproduce the issue

circuit = cirq.Circuit(cirq.X(q[0]))
circuit.insert_at_frontier(cirq.GlobalPhaseOperation(1j), 1)

Traceback (most recent call last):
  File "/Users/tanujkhattar/opt/anaconda3/envs/cirq/lib/python3.8/site-packages/IPython/core/interactiveshell.py", line 3417, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-42-59dcb891d749>", line 2, in <module>
    circuit.insert_at_frontier(cirq.GlobalPhaseOperation(1j), 1)
  File "/Users/tanujkhattar/quantum/Cirq/cirq-core/cirq/circuits/circuit.py", line 2119, in insert_at_frontier
    insertion_indices, _ = self._pick_inserted_ops_moment_indices(flat_ops, start, frontier)
  File "/Users/tanujkhattar/quantum/Cirq/cirq-core/cirq/circuits/circuit.py", line 2014, in _pick_inserted_ops_moment_indices
    op_start = max(start, max(frontier[q] for q in op.qubits))
ValueError: max() arg is an empty sequence

Cirq version
0.12.0.dev
@tanujkhattar tanujkhattar added kind/bug-report Something doesn't seem to work. good first issue This issue can be resolved by someone who is not familiar with the codebase. A good starting issue. area/circuits complexity/low introduces/modifies 1-2 concepts, should take 1-2 days max for an advanced contributor labels Jun 17, 2021
@cduck
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cduck commented Jun 17, 2021 •
edited

I just ran into this bug earlier today (and added a one-line fix for it in #4224).

@cduck cduck mentioned this issue Jun 17, 2021
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@tanujkhattar tanujkhattar added the triage/accepted there is consensus amongst maintainers that this is a real bug or a reasonable feature to add label Jun 19, 2021
CirqBot pushed a commit that referenced this issue Jul 7, 2021
@cduck
Add Circuit Optimizer for sqrt-iSWAP (#4224)
d850bd0 
Follow up to #4213.  Fixes #4083.  (Also contains a one-line change to fix #4225.)

I'm open to name suggestions for `MergeInteractionsToSqrtIswap`.
rht pushed a commit to rht/Cirq that referenced this issue May 1, 2023
@cduck @rht
Add Circuit Optimizer for sqrt-iSWAP (quantumlib#4224)
e96e3e8 
Follow up to quantumlib#4213.  Fixes quantumlib#4083.  (Also contains a one-line change to fix quantumlib#4225.)

I'm open to name suggestions for `MergeInteractionsToSqrtIswap`.
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area/circuits complexity/low introduces/modifies 1-2 concepts, should take 1-2 days max for an advanced contributor good first issue This issue can be resolved by someone who is not familiar with the codebase. A good starting issue. kind/bug-report Something doesn't seem to work. triage/accepted there is consensus amongst maintainers that this is a real bug or a reasonable feature to add
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Add Circuit Optimizer for sqrt-iSWAP cduck/Cirq
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@cduck @tanujkhattar