Integrating \int xJ_0(ax)J_0(bx)dx w/ Bessel Functions

In summary, the conversation is about finding the integral of a function involving the zeroth order Bessel function, and using tools like Mathematica or Wolfram Alpha to solve it. The input format for Wolfram Alpha is the same as Mathematica, and the steps can be obtained by starting with the integral formulation of the Bessel functions and integrating by parts.
  • #1
MarkovMarakov
33
1

Homework Statement


How do I integrate [itex]\int_0^1 xJ_0(ax)J_0(bx)dx[/itex] where [itex]J_0[/itex] is the zeroth order Bessel function?

Homework Equations


See above.
Also, the zeroth order Bessel equation is [itex](xy')'+xy=0[/itex]

The Attempt at a Solution


Surely we must use the fact that [itex]J_0[/itex] is a Bessel function, since we can't integrate any old function in the given integral. But I don't know how.

Thanks for any help.
 
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  • #2
If you're like me, you look it up, either online, or using a tool like Mathematica. Wolfram Alpha is a good online source, and it gave the following answer:

http://www.wolframalpha.com/input/?i=Integrate[x+BesselJ[0%2C+a+x]+BesselJ[0%2C+b+x]%2C+{x%2C+0%2C+1}]
 
  • #3
Thank you @phyzguy. I tried it out but it doesn't seem to be working. What should the inout format be?
 
  • #4
The input should be:

Integrate[x BesselJ[0, a x] BesselJ[0, b x], {x, 0, 1}]

The output is:

(a BesselJ[0, b] BesselJ[1, a] -
b BesselJ[0, a] BesselJ[1, b])/(a^2 - b^2)

which is [tex]\frac{a J_0(b) J_1(a) - b J_0(a) J_1(b)}{a^2-b^2}[/tex]
 
  • #5
@phyzguy: Thanks! :-) How did you figure out the inout format for WA? Do you know how I can get the steps as well?
 
  • #6

Related to Integrating \int xJ_0(ax)J_0(bx)dx w/ Bessel Functions

1. How do I integrate the product of two Bessel functions?

To integrate the product of two Bessel functions, you can use the identity J0(ax)J0(bx) = (1/2)[J0(a+b)x + J0(a-b)x]. This simplifies the integral to a sum of two simpler integrals which can be evaluated using standard integration techniques.

2. Can this integration be done by hand?

Yes, this integration can be done by hand using the identity mentioned above and standard integration techniques. However, it may be more efficient to use a computer program or calculator for more complicated integrals.

3. What are some practical applications of integrating Bessel functions?

Bessel functions have many practical applications in physics, engineering, and mathematics. They are commonly used to describe wave phenomena, such as electromagnetic waves and sound waves. They also have applications in signal processing, quantum mechanics, and heat transfer.

4. Are there any special cases to consider when integrating Bessel functions?

Yes, there are a few special cases to consider when integrating Bessel functions. For example, if a or b is equal to zero, the integral becomes simpler and can be evaluated using basic integration techniques. Additionally, if a and b are both integers, the integral may have a closed form solution in terms of other special functions.

5. Are there any other methods for integrating Bessel functions?

Yes, there are other methods for integrating Bessel functions, such as using contour integrals or series expansions. These methods may be more useful for evaluating integrals with complex or non-integer parameters. However, the method of using the identity J0(ax)J0(bx) = (1/2)[J0(a+b)x + J0(a-b)x] is the most commonly used and efficient method for integrating the product of two Bessel functions.

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