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Re: Problem with evaluation of Besel Functions

• To: mathgroup at smc.vnet.net
• Subject: [mg55984] Re: [mg55963] Problem with evaluation of Besel Functions
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Wed, 13 Apr 2005 01:10:08 -0400 (EDT)
• Reply-to: hanlonr at cox.net
• Sender: owner-wri-mathgroup at wolfram.com

BesselJ[1.5,0]

0.

(BesselJ[x,y]/.y->0)/.x->1.5

0.

BesselJ[3/2,y]

(Sqrt[2/Pi]*(Sin[y]/y - Cos[y]))/Sqrt[y]

You need to use a Limit

Limit[BesselJ[x,y]/.x->3/2,y->0]

0

Limit[BesselJ[x,y]/.x->Rationalize[1.5],y->0]

0


Bob Hanlon

> 
> From: Ariel sumeruk <ariel.sumeruk at gmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/04/12 Tue AM 05:26:14 EDT
> To: mathgroup at smc.vnet.net
> Subject: [mg55984] [mg55963] Problem with evaluation of Besel Functions
> 
> Hello
> I am having a problem evaluating various functions, One example is the 
following
> 
> BesselJ[1.5, 0] evaluates to 0 but
> (BesselJ[xx, yyy] /. xx -> 1.5) /. yyy -> 0 evaluates to complex infinity
> 
> I seem to encounter many of these problems with Bessel and Legendre
> functions where I get actual diffrent numerical results depending on
> How I set the parameters.
> Thanks for anyone who might help
> Ariel
> 
>