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Equation 5 · Part 3 · The Valley of Stability Is a Fitness Landscape

Symbol Z

A=N+ZA = N + Z
ZZ

What this part means

the mass number.

Its job in the formula

Z is one of the signed contributions combined to compute the quantity on the left.

Where the article explains it

The quantity that plays fitness’s role has a name in nuclear physics already: binding energy per nucleon, B(A,Z)/A , where A = N + Z is the mass number.

The passage around this formula

The quantity that plays fitness’s role has a name in nuclear physics already: binding energy per nucleon, B(A,Z)/A , where A = N + Z is the mass number. It is the energy that would have to be supplied to disassemble a nucleus into Z free protons and N free neutrons, divided by the number of nucleons, and a higher value means a more tightly bound, lower-energy configuration — precisely the sense in which a fitness function…

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Learn the underlying idea

A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the surrounding passage

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