Interpolation polynomials and errors.

vendredi 1 novembre 2013

Hi,

1. The problem statement, all variables and given/known data

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.



2. Relevant equations







3. 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[itex]\in[/itex][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 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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