Plotting Lagrange interpolation polynomial

Asked Apr 14 '22 at 16:28

Active Apr 14 '22 at 16:45

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I am writing a code that plots the Lagrange polynomial of a given function. I have all the necessary data, but I can't find a way to plot

$P(x) = \sum_{i=0}^n (f(a_i) \prod_{j\neq i,j=0}^n \frac{x-a_j}{a_i-a_j} )$

Note that I don't want to use pgfplots, since I already know how to do it this way. Using only tikz I find difficult to declare the function to plot. Thank you for your help :)

edited Apr 14 '22 at 16:45

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asked Apr 14 '22 at 16:28

cento18

This looks like a huge expression. I'd use Lua or something-else to compute the coordinates, also avoid possible floating point error etc. – user202729 Apr 15 '22 at 07:31
There's How to use a summation in a tikz plot - TeX - LaTeX Stack Exchange / tikz pgf - Visualizing a function defined through a summation - TeX - LaTeX Stack Exchange . For the product I'm not too sure – user202729 Apr 15 '22 at 07:41

Plotting Lagrange interpolation polynomial

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