Created SumOfProducts subclass of ControlValues #5755
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This class allows the creation of control values that can't be factored into simple products hence solving quantumlib#4512
| nand = SumOfProducts(((0, 0), (0, 1), (1, 0))) # nand of two bits | ||
| """ | ||
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| _internal_representation: Tuple[Tuple[int, ...], ...] |
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Can we add a post init method which verifies that length of all nested tuples in self._internal_representation is the same? This is assumed to be true in the implementation of methods like _number_variables below
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added, I also test for the uniqueness of products in it
cirq-core/cirq/ops/control_values.py
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| return frozenset(self._internal_representation) == {(1,) * self._number_variables()} | ||
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| def diagram_repr(self) -> str: | ||
| return NotImplemented |
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Why is the diagram_repr not implemented?
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the most basic implementation is problematic since the strings will be quite large since they have size num_products x num_qubits => O(num_qubits x 2^num_qubits), this is why I'm hestiant to implement it, however I added it anyway :)
cirq-core/cirq/ops/control_values.py
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| def __getitem__( | ||
| self, key: Union[int, slice] | ||
| ) -> Union['AbstractControlValues', Tuple[int, ...]]: | ||
| return NotImplemented |
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Why is this NotImplemented? Also, I don't like the pattern of
a) Declaring abstract methods in the API, telling the users that all implementations will implement these abstract methods.
b) Returning NotImplemented in the implementation of the abstract methods.
If we want to allow implementations to return NotImplemented; then these shouldn't be abstract methods in the first place.
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the reason that I'm hesitant to implement it is that it will have a different meaning from that of ProductOfSums, where in ProductOfSums we get valide values of qubit, here we get a product
| if not isinstance(other, SumOfProducts): | ||
| raise TypeError( | ||
| f'And operation not supported between types SumOfProducts and {type(other)}' | ||
| ) |
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We are not doing the the linked-list style concatenation discussed earlier? Will that come in a follow-up PR?
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I would wait until next PR, I want to introduct the SumOfProducts class before Cirq 1.0, because it has full expressive power (i.e. fixes the original issue), the linked structure can be introducted later without affecting users
the difference between the current state and what will happen when the linked structure is introduced is expressions like this ((x xor y) and (z and w)) and can now be represented by a SumOfProducts objects that has 8 products, while when we introduce the linked structure then we will only need to store 5 products (2 for the first and 3 for the second) and similarly for larger expressions where we would could in some cases store an exponenetial number of products in pseudopolynomial space.
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The doctests are failing because they run the python expression in docstrings written within ">>>" code blocks and compare the expected ouptut with received output.
I've suggested changes that should fix the failing tests. See https://docs.python.org/3/library/doctest.html for more details.
cirq-core/cirq/ops/control_values.py
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| This can be constructed as | ||
| >>> xor_control_values = cirq.SumOfProducts(((0, 0), (1, 1))) | ||
| >>> q0, q1, q2 = cirq.LineQubit.range(3) | ||
| >>> cirq.X(q2).controlled_by(q0, q1, control_values=xor_control_values) |
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| >>> cirq.X(q2).controlled_by(q0, q1, control_values=xor_control_values) | |
| >>> xor_cop = cirq.X(q2).controlled_by(q0, q1, control_values=xor_control_values) |
cirq-core/cirq/ops/control_values.py
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| >>> nand_control_values = cirq.SumOfProducts(((0, 0), (0, 1), (1, 0))) | ||
| >>> q0, q1, q2 = cirq.LineQubit.range(3) | ||
| >>> cirq.X(q2).controlled_by(q0, q1, control_values=nand_control_values) |
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| >>> cirq.X(q2).controlled_by(q0, q1, control_values=nand_control_values) | |
| >>> nand_cop = cirq.X(q2).controlled_by(q0, q1, control_values=nand_control_values) |
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@tanujkhattar I fixed the docstring and added the optional argument to diagram_repr that we discussed offline |
…moved indexing from abstract class
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@tanujkhattar I added the changes we discussed offline namely I did't get to testing ControlledOperations/Gates with SumOfProducts, however it should work fine, however I know of a line that will break (and worse silently) with SumOfProducts and that is this one https://github.com/quantumlib/Cirq/blob/master/cirq-core/cirq/ops/controlled_operation.py#L170 the comparison logic will break I tried a quick fix but it didn't work, I think in a follow up in which we add the tests we discussed we will also need to fix this line |
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@NoureldinYosri Thanks for the changes; I'll merge this PR and implement the additional fixes. Have a safe trip! |
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This class allows the creation of control values that can't be factored into simple products hence solving quantumlib#4512
This class allows the creation of control values that can't be factored into simple products hence solving #4512