MATH 435 Homework 5: Approximation of Functions using Legendre and Chebyshev Polynomials -, Assignments of Mathematical Methods for Numerical Analysis and Optimization

A math homework assignment for math 435, where students are required to find least-squares approximations and interpolating polynomials using legendre and chebyshev polynomials. The problems involve finding the coefficients for the approximations, locating the zeros and extreme points of chebyshev polynomials, and constructing interpolating polynomials. The document also includes problems on finding the expressions for the coefficients of chebyshev least-squares approximations and minimizing the error between polynomials.

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Pre 2010

Uploaded on 08/18/2009

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Homework #5 MATH 435 Prof. B. Datta
SP09
Due Friday, April 10, 2009
1. (a) Using Legendre polynomials of degree 1, 2, and 3, find the least-squares approxi-
mation for the function exon [2,4].
(b) Find the quadratic least-squares approximation for f(x) = sin π(x) on [0,1] using
Chebyshev polynomials.
1
pf3
pf4

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Homework #5 MATH 435 Prof. B. Datta

SP

Due Friday, April 10, 2009

  1. (a) Using Legendre polynomials of degree 1, 2, and 3, find the least-squares approxi- mation for the function e−x^ on [2, 4].

(b) Find the quadratic least-squares approximation for f (x) = sin π(x) on [0, 1] using Chebyshev polynomials.

  1. (a) Show that the Chebyshev polynomial Tk(x) of degree k ≥ 1 has k simple zeros in the interval [− 1 , 1] at

xj = cos

2 j − 1 2 k

π

, j = 1, 2 ,... , k

and Tk(x) has extreme points at zj = cos

jπ k

, j = 0, 1 ,... , k.

(b) What are the optimal nodes for interpolating with a polynomial of degree 2 on [2, 5]?

(c) Using the zeros of T˜ 3 (x), construct an interpolating polynomial of degree 2 for f (x) = ex^ on [2, 5].

  1. Using the 4th degree polynomial p 4 (x) for sin x (obtained from a power series expan- sion), find a polynomial p 3 (x) of degree 3 such that

max 1 ≤x≤ 1 |p 4 (x) − p 3 (x)|

will be minimum. What is the total error (sum of the truncation error + error by Cheysher approxima- tion)?