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Counterexample

Is this true?

Increasing the number of equally spaced interpolation nodes improves the approximation

No — it is false.

The counterexample

Runge's function 1/(1+25x2)1/(1 + 25x^{2}) on [−1, 1]

Why it fails

The interpolants diverge near the endpoints as n→∞n \to \infty. Chebyshev nodes restore convergence.

Go deeper· Explained in full in Interpolation and numerical integration· Asked in CSIR NET June 2025· From Numerical Analysis › Interpolation and numerical integration with error terms

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