Chebshev polynomial approximation

In summary, the conversation is about finding a polynomial approximation to a given function using Chebyshev polynomials and MATLAB. The attempt at a solution involves using a substitution and noting a certain property of the Chebyshev polynomials. However, the desired numerical value is not obtained and an error message appears. The speaker is seeking help with this issue.
  • #1
sbashrawi
55
0

Homework Statement



Hi every body

I am triyng to find a polynolial approximation to the function: f(x)= (x+2)ln(x+2)
using the chebyshev polynomials,
the idea is to use MATLAB to find the coeefficients of the approximation poly.
using the comand double(int(...))
but this command doesn't give me any numerical value
Waht I got was:
>> int((x+2)*log(x+2)*(1-x^2)^-0.5,-1,1)
Warning: Explicit integral could not be found.
ans =
int((log(x + 2)*(x + 2))/(1 - x^2)^(1/2), x = -1..1)
>>
and if I use double(int(...)) an error message shows up
Any help pls

Homework Equations





The Attempt at a Solution

 
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  • #2
Consider the substitution [itex]x=\cos(\theta)[/itex] and note that [itex]T_k(x) = \cos(k \,\theta)[/itex]. This should remove the singularity.
 

1. What are Chebyshev polynomials?

Chebyshev polynomials are a set of orthogonal polynomials that are commonly used in mathematical and scientific applications for approximating functions. They are named after the Russian mathematician Pafnuty Chebyshev and have various properties that make them useful in numerical analysis and approximation.

2. How are Chebyshev polynomials calculated?

Chebyshev polynomials can be calculated using a recurrence relation or a generating function. The recurrence relation for the Chebyshev polynomials of the first kind is Tn+1(x) = 2xTn(x) - Tn-1(x), where T0(x) = 1 and T1(x) = x. The generating function for the Chebyshev polynomials of the first kind is (1 - 2xt + t2)-1.

3. What is the purpose of Chebyshev polynomial approximation?

Chebyshev polynomial approximation is used to approximate a given function using a finite number of Chebyshev polynomials. This is useful because Chebyshev polynomials have the property of minimizing the maximum error between the approximation and the original function. This makes them particularly useful in cases where a high degree of accuracy is required.

4. How is Chebyshev polynomial approximation different from other types of approximation?

Chebyshev polynomial approximation differs from other types of approximation, such as Taylor series or Fourier series, in that it minimizes the maximum error rather than the average error. This makes it a better choice for approximating functions with sharp changes or discontinuities, as it can provide a more accurate representation of the function in these areas.

5. What are some applications of Chebyshev polynomial approximation?

Chebyshev polynomial approximation has various applications in mathematics, physics, and engineering. Some examples include numerical integration, solving differential equations, signal processing, and image compression. They are also commonly used in computer graphics and animation for approximating smooth curves and surfaces.

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