I am new in Mathematica, I try to find the following numerical integral. but I get the error message ( NIntegrate failed to converge to prescribed accuracy ...), I know that there is a divergence since there is a rho in the denominator of the fraction but how can I solve that?I think I should transform the integral any help? can any one transform the integral for me

   f[l_] :> {0, ((155*2)/ρ)*
        BesselJ[l, 23*y]^2*y, {y, 0, ρ}], (6.75*2*l*
         Integrate[BesselJ[l, 23*y]^2/y, {y, ρ, Infinity}])/
       10^2} . 
           {0, -D[(6.75*2*l*
           Integrate[BesselJ[l, 23*y]^2/y, {y, ρ, Infinity}])/
         10^2, ρ], (1/ρ)*
            BesselJ[l, 23*y]^2*y, {y, 
             0, ρ}]), ρ]}], {ρ, 0, Infinity}, 
   WorkingPrecision -> 10]
  • 5
    $\begingroup$ Please edit your question: prior to copy and paste, convert your cell to InputForm (or Raw InputForm) $\endgroup$
    – Bob Hanlon
    Commented Aug 17, 2022 at 23:08
  • $\begingroup$ How I edit that? $\endgroup$
    – sara
    Commented Aug 19, 2022 at 11:03
  • 1
    $\begingroup$ Click on the word Edit below the question $\endgroup$
    – Bob Hanlon
    Commented Aug 19, 2022 at 13:40

1 Answer 1


Step 1. The expression provided by OP can be cleaned up a bit. For example, this is a subexpression of the expression provided by OP, with the exception that I put an Inactive in to get Mathematica to exploit the fact that there is derivative D just outside:


This simplifies to


Step 2. Doing Step 1 for the entire integrand that OP has provided, I get the following simpler formula for the integrand, where I also replaced 41.85 by 4185/100 to avoid problems with floating point numbers:

integrand[l_]:=integrand[l]=Assuming[ρ>0, 4185/100 l BesselJ[l, 23 ρ]^2 (
    ρ^2 Integrate[BesselJ[l, 23 y]^2/y, {y, ρ, \[Infinity]}]
    + Integrate[y BesselJ[l, 23 y]^2, {y, 0, ρ}])/ρ//Simplify];

This can be evaluated. For example, taking the value l==5 in the question:

(* (1/(1566219705620 ρ^7))837 (529 ρ^2 (-4608 + 
      101568 ρ^2 - 5596820 ρ^4 + 
      740179445 ρ^6) BesselJ[0, 23 ρ]^2 - 
   23 ρ (-18432 + 1625088 ρ^2 - 22387280 ρ^4 + 
      740179445 ρ^6) BesselJ[0, 23 ρ] BesselJ[1, 
     23 ρ] + (-18432 + 2843904 ρ^2 - 102981488 ρ^4 - 
      2960717780 ρ^6 + 391554926405 ρ^8) BesselJ[1, 
     23 ρ]^2) BesselJ[5, 23 ρ]^2 *)

Step 3. Let us plot this:


This gives

enter image description here

Looks nice, but decay seems slow. In fact, let us also plot ρ times the integrand:


This gives

enter image description here

It seems likely that this oscillates forever with some fixed amplitude (see remark below). Thus integrand[5] is 1/ρ times this oscillation. That is too slow for convergence of the integral over {ρ,0,\[Infinity]}. Hence the integral does in fact not converge, it is $+\infty$.

The divergence is not due to the behavior near ρ==0, in fact the integrand decays quickly towards ρ==0. Rather, the divergence is due to slow decay as ρ goes to infinity.

Remark. The 1/ρ decay is due to the following terms in integrand[5]//Expand:

  ρ BesselJ[0, 23 ρ]^2 BesselJ[5, 23 ρ]^2
  ρ BesselJ[1, 23 ρ]^2 BesselJ[5, 23 ρ]^2
  • $\begingroup$ following your step, I get this result in step 2 (Assuming[[Rho] > 0, {0, (310/[Rho])* Integrate[ BesselJ[l, 23*y]^2*y, {y, 0, [Rho]}], ((675/100)*2*l* Integrate[BesselJ[l, 23*y]^2/y, {y, [Rho], Infinity}])/10^2} . {0, (0.135*l*BesselJ[l, 23*[Rho]]^2)/[Rho], 310*BesselJ[l, 23*[Rho]]^2}]). $\endgroup$
    – sara
    Commented Aug 23, 2022 at 11:42

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