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MathGroup Archive 2002

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RE: List, FindRoot, Bessel

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33632] RE: [mg33628] List, FindRoot, Bessel
  • From: "David Park" <djmp at earthlink.net>
  • Date: Thu, 4 Apr 2002 19:39:49 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Riadh,

k -> 3.2 is a rule. Mathematica usually provides the solution to equations
in the form of rules. To learn more how this works check out Solve in Help
and Section 1.5.7 in The Mathematica Book.

If we write:

k /. k -> 3.2     we get
3.2  where /. means replace k using the rule.

The simplest method to create a list of objects is to use the Table command.
To obtain a list of the solutions to your equations we simply use:

Table[k /.
    FindRoot[- k BesselJ[1, k] + 30 BesselJ[0, k] == 0, {k, 2.32 + i Pi}],
 {i, 0, 9}]
{2.32614, 5.34098, 8.37707, 11.4221, 14.4748, 17.5348, 20.602, 23.6762,
26.7568, 29.8435}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

> -----Original Message-----
> From: Riadh Alimi [mailto:alimir3 at cti.ecp.fr]
To: mathgroup at smc.vnet.net
> Sent: Wednesday, April 03, 2002 6:09 PM
> Subject: [mg33632] [mg33628] List, FindRoot, Bessel
>
>
> Hi !
>
> I'm trying to find the first n roots of an equation involving Bessel
> Functions and to create a List of them.
>
> The best thing I find so far is :
> n = 10;
> For[i = 0, i < n,
>   Print[FindRoot[- k BesselJ[1, k] + 30 BesselJ[0, k] == 0, {k,
>         2.32 + i Pi}]];
>   i++]
>
> And the result I get is :
>
> {k->3.2}
> {k->5.2}
> {k->8.3}
> ....
>
> Does anyone know what {k->3.2} means ? And how I could get only the value
> 3.2 instead of {k->3.2} in order to create a list?
>
> Thank you
>
>
>



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