Interpolation polynomials and errors.

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SUMMARY

The discussion focuses on bounding the error in quadratic piecewise interpolation for the function f(x) = cos(πx) over evenly distributed nodes in the interval [0,1]. The proposed error bound is |e(x)| ≤ [1/(n+1)!]max(f(n+1)(c))*max(∏[i=0,n](x-xi)), leading to a specific error estimate of [1/3!]*π³*2h³/(3√3). The user seeks clarification on the correctness of this bound and its distinction from error bounds for other functions, such as f(x) = e^(-x).

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peripatein
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Hi,

Homework Statement


A quadratic piecewise interpolation is carried out for the function f(x)=cos(πx) for evenly distributed nodes in [0,1] (h=xi+1-xi, xi=ih, i=0,1,...,πh).
I am asked to bound the error.

Homework Equations


The Attempt at a Solution


I believe the error in this case is bounded thus:
|e(x)| ≤ [1/(n+1)!]max(f(n+1)(c))*max(∏[i=0,n](x-xi))
where c\in[0,1]
hence, yielding [1/3!]*π3*2h3/(3√3)
(1) First of all, is that correct?
(2) Next, in case this is correct, why is it bounded thus instead of as in the case for f(x)=e-x in [0,1] where, generally, it is bounded thus:
|e(x)| ≤ hn+1/(4*(n+1))
??
I'd sincerely appreciate some insight, please.
 
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