Equation 1 · Part 4 · Reactor Phylogenetics: The Family Tree of Fission Power

Symbol n_B

P(\text{next adopter} = A \mid n_A, n_B) = \frac{n_A + a}{n_A + n_B + a + b}

n_B

What this part means

cumulative past adoptions and a.

Its job in the formula

$n_B$ occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

Full expressionSymbol n_BArticle meaning

Where the article explains it

where $n_A$ and $n_B$ are cumulative past adoptions and a, b are small initial weights representing early, largely arbitrary advantages [ 2 ] .

The passage around this formula

…generalized Pólya urn: two technologies accumulate adopters, and the probability the next adopter chooses technology A over B is proportional to how many adopters A already has, so that $P(\text{next adopter} = A \mid n_A, n_B) = \frac{n_A + a}{n_A + n_B + a + b}$ . where $n_A$ and $n_B$ are cumulative past adoptions and a, b are small initial weights representing early, largely arbitrary advantages [ 2 ] . Once $n_A$ pulls ahead by chance or by an unrelated advantage — a submarine program’s development budget, say — the process is self-reinforcing regardless of whether A is the…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the surrounding passage

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