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Equation 9 · The Network Is the Computer Again

What does this equation mean?

T(n,p)=α L(p)+β W(n,p)+γ C(n,p),T(n,p) = \alpha\,L(p) + \beta\,W(n,p) + \gamma\,C(n,p),

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Inputs and operationsalphaL(p) + betaW(n,p) + gammaC(n,p)
Result or conditionT(n,p)
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This equation states an equality: the expressions on both sides have the same value under the article’s assumptions. Read the equation part by part below; each part has a contextual explanation and a link to its mathematical background.

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TT

Symbol T

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

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nn

Symbol n

n is an argument of the function-like quantity on the left; its role is set by that function’s stated inputs.

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pp

Symbol p

p is an argument of the function-like quantity on the left; its role is set by that function’s stated inputs.

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α\alpha

Symbol α

the writing.

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LL

Symbol L

L is one of the signed contributions combined to compute the quantity on the left.

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β\beta

Symbol β

β is one of the signed contributions combined to compute the quantity on the left.

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WW

Symbol W

W is one of the signed contributions combined to compute the quantity on the left.

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γ\gamma

Symbol gamma

gamma is one of the signed contributions combined to compute the quantity on the left.

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CC

Symbol C

C is one of the signed contributions combined to compute the quantity on the left.

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=

=

The expressions on both sides represent the same quantity under the stated assumptions.

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addition

addition

Add the term after the plus sign to the term or group before it.

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How to interpret it

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What the article says around this equation

The classical accounting for a collective operation separates three terms: a per-message latency, a per-byte transfer cost, and a per-byte computation cost for reductions [ 2 ] . Writing α\alpha for latency per message, β\beta for transfer time per byte and γ\gamma for reduction time per byte, the cost of a collective over p participants on n bytes takes the shape T(n,p)=α L(p)+β W(n,p)+γ C(n,p)T(n,p) = \alpha\,L(p) + \beta\,W(n,p) + \gamma\,C(n,p). where L counts message steps, W counts bytes crossing each link and C counts arithmetic. The whole art of collective algorithm design is choosing which of these terms to pay.

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