What Is an Example of a Nonintegrable Bounded Function?

In summary, a function that is bounded but nonintegrable is one that is either discontinuous on a set of points with measure 0 (Riemann integrability) or discontinuous everywhere (Lebesgue integrability). This can be seen in the examples provided, such as the Dirichlet function and the function that is 0 for irrational numbers and 1 for rational numbers. However, it is important to note that continuity is not a necessary condition for integrability, but rather a sufficient one.
  • #1
matrix_204
101
0
could someone give me an example of a function that is bounded but is nonintegrable?


i need to know what a nonintegrable function bounded on [a,b] is as said in my preperation file for a test? urgent help needed
 
Last edited:
Physics news on Phys.org
  • #2
How about
[tex] f:(0,1)\rightarrow R [/tex],

[tex] f(x)=0,x\in ((0,1) \cap R-Q) [/tex]

[tex] f(x)=1,x\in ((0,1) \cap Q) [/tex]

Daniel.
 
  • #3
yup thnx, i forgot we did an example of dirichilet function in class, this function is an example of a lot of things used in calculus, lol,
 
  • #4
Always remember that continuity is a necessary condition for integrability...

Daniel.
 
  • #5
Continuity is a sufficient condition for integrability, not a necessary one. A function that is discontinuous on a set of points of measure 0 is integrable, and vice versa (i.e. this gives a necessary and sufficient condition). Clearly, a continuous function is discontinuous on an empty set which of course has measure 0, so it is integrable. The example you gave is discontinuous on (0, 1), a set that doesn't have measure 0, which is why f is not integrable. Of course, this also depends on how you define integration and integrability.
 
Last edited:
  • #6
Are u talking about Lebesgue,or Riemann integrability...?

Daniel.
 
  • #7
dextercioby: The function f(x)= 0 if x< 0; 1 if 0< x< 1; 0 if x> 1 is (Riemann) integrable over any interval but is not continuous at 0 and 1.

The function: f(x)= 0 if x is rational; 1 if x is irrational is (Lebesque) integrable over any interval but is not continuous anywhere.
 
  • #8
AKG's right, I'm pretty sure. IIRC, A bounded function is Riemann integrable over a compact set iff it's discontinuous on a set of measure zero.
 
  • #9
Got it.Thank you.

Daniel.
 

FAQ: What Is an Example of a Nonintegrable Bounded Function?

What is a nonintegrable bounded function?

A nonintegrable bounded function is a mathematical function that cannot be integrated using traditional integration techniques. This means that there is no closed-form solution for the integral of the function, and it must be approximated using numerical methods.

How is a nonintegrable bounded function different from a regular bounded function?

A regular bounded function can be integrated using traditional methods, while a nonintegrable bounded function cannot. This is because the nonintegrable function may have discontinuities or other complexities that prevent a closed-form solution.

What are some real-world applications of nonintegrable bounded functions?

Nonintegrable bounded functions are commonly used in physics and engineering to model systems that exhibit chaotic or unpredictable behavior. They are also used in economics and finance to model stock prices and other complex systems.

How can nonintegrable bounded functions be approximated?

Nonintegrable bounded functions can be approximated using numerical integration techniques, such as the Trapezoidal Rule or Simpson's Rule. These methods divide the function into smaller segments and approximate the area under the curve using linear or polynomial approximations.

Can a nonintegrable bounded function ever be integrated exactly?

No, a nonintegrable bounded function cannot be integrated exactly. However, it can be approximated to any desired level of precision using numerical integration techniques.

Back
Top