Can the Fejér Kernel Be Approximated by Polynomials?

In summary, the Approximate Fejér kernel is a mathematical function used in Fourier analysis to approximate periodic functions by a finite sum of simpler functions. It is defined as the average of the Dirichlet kernels and has properties such as continuity, positivity, and symmetry. It is related to the Fejér kernel and is commonly used in various applications such as signal processing, image reconstruction, and data compression.
  • #1
Vannel
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TL;DR Summary
Methods to approximate Fejér kernel
Hello, I'm currently studying the Fejér kernel, which has the form of
F_{n}(x)={\frac  {1}{n}}\left({\frac  {\sin {\frac  {nx}{2}}}{\sin {\frac  {x}{2}}}}\right)^{2}={\frac  {1}{n}}\left({\frac  {1-\cos(nx)}{1-\cos x}}\right)
. I want to know whether there are some methods to approximate this function into polynomials.

Thanks a lot for the help!
 
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  • #2
Take a look here:

https://en.wikipedia.org/wiki/Fejér_kernel
We can rewrite the kernel as a sum of exponentials, and exponentials are easily approximated by polynomials (take some terms of their series expansion). Thus we can approximate the kernel as well.

Alternatively, you can use results like Stone-Weierstrass.
 

1. What is the Fejér Kernel?

The Fejér Kernel is a mathematical function used in Fourier analysis. It is defined as the average of the Dirichlet kernels, which are a set of periodic functions commonly used in the study of Fourier series.

2. How is the Fejér Kernel related to polynomials?

The Fejér Kernel can be approximated by polynomials through a process called polynomial interpolation. This involves finding a polynomial function that closely matches the Fejér Kernel over a specific interval.

3. Why is it important to approximate the Fejér Kernel by polynomials?

Approximating the Fejér Kernel by polynomials allows for easier computation and analysis of Fourier series. Polynomials are also more manageable and easier to manipulate than the Fejér Kernel itself, making it a useful tool in mathematical calculations.

4. Is it possible to accurately approximate the Fejér Kernel by polynomials?

Yes, it is possible to accurately approximate the Fejér Kernel by polynomials. However, the accuracy of the approximation depends on the degree of the polynomial used and the interval over which it is being approximated.

5. What are some applications of approximating the Fejér Kernel by polynomials?

Approximating the Fejér Kernel by polynomials has various applications in mathematics, physics, and engineering. It is commonly used in signal processing, image reconstruction, and data analysis. It also has applications in solving differential equations and studying periodic functions.

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