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indexing in the formula for phi_j#25

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ShawnL00 wants to merge 2 commits intoinducer:mainfrom
ShawnL00:patch-2
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indexing in the formula for phi_j#25
ShawnL00 wants to merge 2 commits intoinducer:mainfrom
ShawnL00:patch-2

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@ShawnL00
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#+LATEX: \begin{hidden}
Easier to build than Lagrange, but: coefficient finding costs \(O (n^2)\).
\[\varphi _j (x) = \prod _{k = 1}^{j - 1} (x - x_k) . \]
\[\varphi _j (x) = \prod _{k = 1}^{j} (x - x_k) . \]
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Technically, that depends on the numbering. I would agree with your change if the numbering started at zero:

Suggested change
\[\varphi _j (x) = \prod _{k = 1}^{j} (x - x_k) . \]
\[\varphi _j (x) = \prod _{k = 1}^{j} (x - x_k) . \qquad (j\in\{0,\dots,n-1\})\]

but then that's inconsistent with Lagrange.

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My counterproposal to this is in #26. Could you take a look?

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inducer commented Mar 28, 2026

Closing in favor of #26.

@inducer inducer closed this Mar 28, 2026
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