Equation 8 · Part 12 · The Valley of Stability Is a Fitness Landscape
fraction
fraction
What this part means
Divide the expression above the line by the one below it.
Its job in the formula
The expression above the fraction bar is divided by the complete expression below it. The denominator must not be zero.
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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 assigns a scalar payoff to a state. The theoretical account of how that payoff varies across the chart is the semi-empirical mass formula, first written down by Carl Friedrich von Weizsäcker in 1935 as a liquid-drop model of the nucleus [ 11 ] . In one common form, the…
Learn the underlying idea
A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.
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Sources cited in the surrounding passage
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