← All parts of this equation

Equation 1 · Part 4 · The Hardest Unsolved Problems in Evaluating xAI's Claims

subscript

uk=10k/2,k∈{1,2,3},u_k = 10^{k/2}, \qquad k \in \{1, 2, 3\},
subscript

What this part means

The lower label selects a particular version, component, or indexed member of the quantity. For example, x₀ and xₜ can be values at different positions.

Its job in the formula

A subscript distinguishes a version, component, step, or member of a quantity. It does not automatically mean multiplication.

The passage around this formula

Epoch AI, a research organisation that tracks compute at the frontier, publishes exactly this kind of reconstruction for Colossus and states its own confidence in bands rather than single numbers: an estimate graded “Confident” carries roughly ±3x uncertainty, “Likely” roughly ±10x, and “Speculative” roughly ±31x [ 4 ] . Those three multipliers are not arbitrary; they sit at half-order-of-magnitude steps, uk=10k/2,k∈{1,2,3}u_k = 10^{k/2}, \qquad k \in \{1, 2, 3\}. giving u1u_1 ≈\approx 3.16 , u2u_2 = 10 , and u3u_3 ≈\approx 31.6 — which is a formal way of saying that even a well-resourced independent estimate of a frontier training run can be off by an order of magnitude or more, and everyone doing the estimating knows it going in.…

Read this part in the article →

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 →

Sources cited in the surrounding passage

These citations provide research context; check each source for the exact claim it supports.