cirq.trace_distance_bound

Returns a maximum on the trace distance between this effect's input and output.

cirq.trace_distance_bound(
    val: Any
) -> float

This method attempts a number of strategies to calculate this value.

Strategy 1
Use the effect's `_trace_distance_bound_` method.

Strategy 2
If the effect is unitary, calculate the trace distance bound from the eigenvalues of the unitary matrix.

Args
`val`	The effect of which the bound should be calculated

Returns
If any of the strategies return a result that is not Notimplemented and not None, that result is returned. Otherwise, 1.0 is returned. Result is capped at a maximum of 1.0, even if the underlying function produces a result greater than 1.0

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Last updated 2025-07-23 UTC.

Strategy 1