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Equation 32 · Part 1 · How a Model Actually Gets Small Enough to Run on a Phone

Symbol s

ss
ss

What this part means

the scale.

Its job in the formula

s is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Where the article explains it

The standard affine mapping takes a real value x , a scale s and a zero-point z , and produces an integer xqx_q = clip\mathrm{clip}(⌊xs⌉+z, qmin⁡, qmax⁡)\left(\left\lfloor \frac{x}{s} \right\rceil + z,\ q_{\min},\ q_{\max}\right), \qquad x^\hat{x} = s(xq−z)\left(x_q - z\right) where ⌊\lfloor ⋅\cdot ⌉\rceil is round-to-nearest and x^\hat{x} is the dequantised approximation actually used in arithmetic.

The passage around this formula

so halving the number of bits, which roughly doubles s at fixed range, roughly quadruples the expected squared error per weight. That is why INT8 is usually described as close to free and INT4 is not: the error a network has to absorb does not grow gently as bits are removed, it grows quadratically in the step size, and every bit below eight is removed from an already-narrow budget.

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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 article section

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