Optimizing Polynomial Approximations for Even Functions on Symmetric Intervals

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SUMMARY

The discussion focuses on optimizing polynomial approximations for even functions on symmetric intervals, specifically finding the closest function of the form \( a + bx^3 \) to \( x^2 \) over the interval \([-1, 1]\). The standard inner product used is defined as the integral from -1 to 1 of the product of the functions. The participant's calculations led to a result where the \( x^3 \) term disappears, raising concerns about the validity of the approximation. The discussion emphasizes the importance of considering odd functions in the approximation process to achieve better results.

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  • Understanding of polynomial approximations
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  • Knowledge of even and odd functions
  • Basic calculus, specifically integration techniques
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  • Learn about the properties of even and odd functions in approximation theory
  • Explore the concept of orthogonal functions in inner product spaces
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Homework Statement


find closest function a+bx3 to x2 on the iterval [-1,1]
(we consider standard inner product (f,g) = integral(-1 to 1):fgdx

So, here is my attempt, but I got a suspicious result:

[(1,1) (1,x3)] [a]
[(1,x3) (x3,x3)]
=
[(1,x2)]
[x3, x2)]

then after I've done all the integration I came up with this:
[2 0] [a]
[0 2/7]
=
[1/3]
[0]
which means that x3 term disappears...:frown:
 
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I can't help you fix it. Because you are completely correct. Why do you think that is suspicious? Find ways to check yourself.
 
You are approximating an even function over a symmetric interval. Can adding part of an odd function help you?
 

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