Symbol f
f is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
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Why this formula appears here
There is a fifth kind of answer to “where,” and it is worth stating precisely how it differs from all four above before using it. Prepare a system in a state | , couple it weakly to a pointer, and then postselect on a final state |f measured after the coupling. The weak value of any observable , position among them, conditioned on that postselection is
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Equation 88 · Evolutionary Physics
The Atlas That Refuses to Close
This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text.
There is a fifth kind of answer to “where,” and it is worth stating precisely how it differs from all four above before using it. Prepare a system in a state | , couple it weakly to a pointer, and then postselect on a final state |f measured after the coupling. The weak value of any observable , position among them, conditioned on that postselection is
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