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Start adding coverage for density_matrix_kronecker_product function #7858

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start adding coverage for density_matrix_kronecker_product function
joesho112358 Jan 27, 2026
dce2f08
Merge branch 'main' into density_matrix_kronecker_product_test
joesho112358 Jan 27, 2026
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14 changes: 14 additions & 0 deletions cirq-core/cirq/linalg/transformations_test.py
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Expand Up @@ -665,6 +665,20 @@ def test_factor_state_vector(state_1: int, state_2: int) -> None:
assert np.allclose(b1, b)


def test_density_matrix_kronecker_product() -> None:
matrix_1_array = np.array([[1, 0], [0, 0]], dtype=np.complex64)
matrix_2_array = (
np.array([[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]], dtype=np.complex64) / 4.0
)
matrix_1 = cirq.to_valid_density_matrix(matrix_1_array, qid_shape=(2,), dtype=np.complex64)
matrix_2 = cirq.to_valid_density_matrix(matrix_2_array, qid_shape=(4,), dtype=np.complex64)
calculated_result_shape = tuple(
map(lambda x, y: (x / 2 + y / 2) * 2, matrix_1_array.shape, matrix_2_array.shape)
)
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@joesho112358 joesho112358 Jan 27, 2026 •
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hi @vtomole, i saw you were assigned to this PR automatically and wanted to call out that this is a draft because i am getting:

>       assert matrix_result.shape == calculated_result_shape
E       assert (2, 4, 2, 4) == (6.0, 6.0)

from the assertion that follows. Not sure where my math is failing, but guessing i am not fully understanding the function's docstring

matrix_result = cirq.linalg.transformations.density_matrix_kronecker_product(matrix_1, matrix_2)
assert matrix_result.shape == calculated_result_shape


@pytest.mark.parametrize('num_dimensions', [*range(1, 7)])
def test_transpose_flattened_array(num_dimensions) -> None:
np.random.seed(0)
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