Fourier series convergence question

In summary, we are given a function f(x) and asked to find the x-points where the Fourier series, F(x), fails to converge to f(x). Using the definition of F(x), we can determine that at x = -pi and x = pi, F(x) fails to converge to the values given by f(x). This is because the value of F(x) at these points is not equal to the value of f(x).
  • #1
JamesGoh
143
0

Homework Statement



f(x) = 5, -pi <= x <= 0
f(x) = 3, 0 < x <= pi

f(x) is the function of interest

Find the x-points where F(x) fails to converge
to f(x)


Homework Equations



F(x) = f(x) if f is continuous at [itex]x\in(-L,L)[/itex]
F(x) = 0.5[ f(x-) + f(x+) ] if f is discontinous at [itex]x\in(-L,L)[/itex]

F(x) is the Fourier series of f(x)

The Attempt at a Solution



Would the Fourier series, F(x) fail to converge
at +pi and -pi ?

My reasoning is as follows

- At both -pi and +pi, we have the start and end value of f(x)

- By definition F(x) = (1/2)f(x-) + (1/2)f(x+)

- Let's take x = -pi, which means f(x) =5 and f(-x) = 3

- F(-pi) = (1/2)(5) + (1/2)(3) = 8/2 = 4 which is not equal to f(-pi)=5

- From the latter, we can conclude that F(-pi) fails to converge to
the value given from f(-pi) since their not equal to each other

Just want to check if my reasoning is ok since no answer was provided to this question

thanks
 
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  • #2
Seems ok...
 

Related to Fourier series convergence question

What is a Fourier series and how is it used?

A Fourier series is a mathematical representation of a periodic function as an infinite sum of sine and cosine functions. It is used to approximate functions and analyze their properties.

What does it mean for a Fourier series to converge?

A Fourier series is said to converge when the sum of its terms approaches the value of the function being approximated as the number of terms increases. In other words, the approximation becomes more accurate as more terms are added.

Under what conditions does a Fourier series converge?

A Fourier series will converge if the function being approximated is piecewise continuous and has a finite number of discontinuities in each period. Additionally, the function must have a finite number of maxima and minima in each period.

What is the difference between pointwise and uniform convergence of a Fourier series?

Pointwise convergence refers to the convergence of the Fourier series at individual points, while uniform convergence refers to the convergence of the entire series over a range of values. Uniform convergence is generally considered a stronger form of convergence.

Can a Fourier series converge to a different function than the one it is approximating?

Yes, it is possible for a Fourier series to converge to a different function than the one it is approximating. This is known as Gibbs phenomenon and can occur when the function has discontinuities or sharp corners.

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