Remove dependance of BooleanExpression on tweedledum
#13769
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Pull Request Test Coverage Report for Build 13175136785Warning: This coverage report may be inaccurate.This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.
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Thanks @gadial for taking care of this - it looks great!
Note that there are some necessary API changes here, which makes sense and it's also allowed for Qiskit 2.0, but probably need better release notes, as well as raise deprecation warnings in Qiskit 1.4.
Did you make some experiments to check the performance compared to Tweedledum?
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| @HAS_TWEEDLEDUM.require_in_instance | ||
| class BooleanExpression(ClassicalElement): | ||
| class BooleanExpression(Gate): |
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Note the API change here (changed types)
| quantum register. | ||
| synthesizer: A callable that takes self and returns a Tweedledum | ||
| circuit. | ||
| circuit_type: which type of oracle to create, 'bit' or 'phase' flip oracle. |
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Note the API change in this function
| @@ -50,40 +44,18 @@ class PhaseOracle(QuantumCircuit): | |||
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| def __init__( | |||
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| expression: Union[str, ClassicalElement], | |||
| synthesizer: Optional[Callable[[BooleanExpression], QuantumCircuit]] = None, | |||
| expression: str, | |||
| var_order: list = None, | |||
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Note the API change in the init
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| @HAS_TWEEDLEDUM.require_in_instance | ||
| class BooleanExpression(ClassicalElement): | ||
| class BooleanExpression(Gate): |
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The easiest deprecation path would be to just deprecate BooleanExpression in place and have the new version in the circuit library.
It might also be worth considering a renaming to avoid too much confusion with the new object. What does this circuit implement exactly? Does it flip a target bit if the boolean expression is satisfied or does it something in-place? If it's the first, maybe BitflipOracle could be a good name.
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This seems like a sound strategy - we already have a PhaseOracle so we can add BitFlipOracle which will be similar but with a different synthesis, and both gates would rely on a non-gate version of BooleanExpression (maybe with a different name) which handles parsing, simulating (to create the truth table) and synthesizing (since we might want to invest in optimized algorithms later.
The main question is where to put those files. We can put BitFlipOracle next to PhaseOracle in qiskit.circuit.library but we still need to put the NewBooleanExpression module (which would consist at least of boolean_expression, boolean_expression_visitor and boolean_expression_synth files) somewhere that makes sense.
Summary
Rewrites the
BooleanExpressionclass such that expression parsing and circuit synthesis does not rely on thetweedledumlibrary, and moves it to thesynthesislibrary. Adds aBitFlipOracleclass to preserve the user-facing usage ofBooleanExpression.Partially addresses #13755.
Details and comments
BooleanExpressionis used to describe classical boolean functions and synthesize phase/bit-flip oracles for them. Currently it is used directly within qiskit only for thePhaseOracleclass.The current implementation of
BooleanExpressionrelies on thetweedledumlibrary for parsing and synthesizing. Since qiskit 2.0 will stop usingtweedledum, this PR makes the code ofBooleanExpressionindependent, in the cost of lower capabilities.These are the main changes:
astlibrary, using a customboolean_expression_visitor. Parsing DIMACS files is done directly using regexp.boolean_expression_synthmodule) using a straightforward approach seemingly also employed bytweedledum, given a representation of the function as ESOP (Exclusive sum of squares).BooleanExpressioninto ESOP representation was also added. While it features basic optimizations to reduce the size of the ESOP, it needs to generate the full truth table of the represented function, making it a viable approach only for functions on a relatively low number of variables. This can be improved upon in the future if required, using more sophisticated ESOP generation and minimization techniques (such as using BDDs or SAT-solvers).synthesis/boolean. A new class,BitFlipOraclewas added to the circuit library. The oldBooleanExpressioncode remains unchanged and will be deprecated in a separate PR along with the rest of theclassicalfunctionlibrary.