Symbol q_i

Its job in the formula

$q_i$ is part of the quantity the equation computes from the expression on the right.

Where the article explains it

If a step fails and is retried with probability $q_i$ , independent of other steps, the expected cost of the trajectory becomes $\mathbb{E}$[$C_n$] $\approx$ $\sum_{i=1}^{n}$ $\frac{c_i}{1-q_i}$ Holding $q_i$ = q constant across the trajectory — a simplification, since real failure rates are neither constant nor independent — the expected extra cost from retries is $\frac{q}{1-q}$$\sum_i$ $c_i$ , and because $c_i$ increases with i , that extra cost is weighted toward the trajectory’s most expensive, latest steps rather than distributed evenly across it.

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.

Open the illustrated subscripts: which member of a family? guide →