FA-90897 / Quantum circuit simulation / Member archive

Marginal rounds the numerator before normalizing · case 02

Unnormalized states produce probabilities such as 0.3076923076 with many digits instead of values rounded to 6 decimals.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input [n, amps, qubits]; amps are 2**n [re, im] pairs (qubit 0 = LSB), possibly unnormalized. Return the marginal outcome distribution over the listed qubits as {bitstring: probability} where the first listed qubit is the rightmost character, probabilities are normalized by the total squared norm, rounded to 6 decimals after summation, and zero entries are omitted. Errors: "bad-length", "duplicate-qubit", "bad-qubit", "zero-state" (total squared norm <= 1e-12).

Why this case matters

Marginal readout distributions are what users compare against hardware counts; ordering or normalization slips mislabel every histogram.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: random state 3	`{"00": 0.15768289675589942, "01": 0.19253240034616786, "10": 0.47171717372059707, "11": 0.17806752917733568}`	`{"00": 0.157683, "01": 0.192532, "10": 0.471717, "11": 0.178068}`	Failed

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