Integration of Bessel's functions

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Discussion Overview

The discussion revolves around the integration of Bessel's functions, specifically focusing on the integral \(\int_{0}^{r}\frac{1}{\rho} J_m(a\rho) J_n(b\rho) d\rho\) and its relation to Lommel's integral. Participants explore various approaches to finding a solution and discuss the applicability of recurrence relations and integral representations.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in finding a closed form solution for the integral involving Bessel functions and seeks a foundational approach to the problem.
  • Another participant suggests exploring integral representations of Bessel functions as a potential method to tackle the problem.
  • A different participant proposes the use of recurrence relations to simplify the integral into a more manageable form.
  • A later reply indicates success in applying Lommel's integrals to the problem, confirming their effectiveness through numerical verification in electromagnetic applications.
  • One participant reflects on the utility of special functions, describing their usefulness as akin to "rigorous magic."

Areas of Agreement / Disagreement

Participants do not reach a consensus on a definitive solution to the integral in question. Multiple approaches are suggested, and while some participants find success with Lommel's integrals, others continue to explore different methods.

Contextual Notes

There may be limitations related to the assumptions required for the application of recurrence relations and integral representations, as well as the specific conditions under which Lommel's integrals are applicable.

tworitdash
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TL;DR
For implementing a mode-matching technique in EM simulation, I want to get a closed-form equation of the integral of [tex]\int_{0}^{r}\frac{1}{\rho} J_m(a\rho) J_n(b\rho) d\rho [/tex].
I can only find a solution to \int_{0}^{r} \rho J_m(a\rho) J_n(b\rho) d\rho with the Lommel's integral . The closed form solution to \int_{0}^{r}\frac{1}{\rho} J_m(a\rho) J_n(b\rho) d\rho I am not able to find anywhere. Is there any way in which I can approach this problem from scratch? Here, J_m is the Bessel function of the first kind of order m.
 
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It looks to me like you could use a recurrence relation (see this link) once or twice and arrive at a sum of integrals in the form you know.
 
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Haborix said:
It looks to me like you could use a recurrence relation (see this link) once or twice and arrive at a sum of integrals in the form you know.
Perfect. Thanks! I decomposed my problem and I got the form of Lommel's integrals for all my problems. I verified with numerical solutions for my EM problems and the Lommel's integrals work like magic.
 
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Good to hear! Special functions, when they are useful, always seemed like magic (rigorous magic) to me.
 
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