# cirq.trace_distance_bound¶

cirq.trace_distance_bound(val: Any) → float[source]
Returns a maximum on the trace distance between this effect’s input
and output. This method makes use of the effect’s _trace_distance_bound_
method to determine the maximum bound on the trace difference between
before and after the effect.
Parameters: val – The effect of which the bound should be calculated If val has a _trace_distance_bound_ method and its result is not NotImplemented, that result is returned. Otherwise, 1 is returned. Result is capped at a maximum of 1, even if the underlying function produces a result greater than 1.