Re: Problem with evaluation of Besel Functions
- To: mathgroup at smc.vnet.net
- Subject: [mg56064] Re: Problem with evaluation of Besel Functions
- From: "adamizer" <adam.smith at hillsdale.edu>
- Date: Thu, 14 Apr 2005 08:56:18 -0400 (EDT)
- References: <d3g8kd$smh$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Many have noted the difference between using 3/2 vs 1.5
However there is another aspect to your post that I noticed. The
result depends on exactly how you do the substitution. Reversing the
order avoids the complex infinity, indeterminate problem.
Look at:
(BesselJ[xx, yyy] /. xx -> 1.5) /. yyy -> 0
Returns ComplexInfinity (or Inderterminate for xx->3/2)
versus doing it in the other order:
(BesselJ[xx, yyy] /. yyy -> 0) /. xx -> 1.5
Returns 0. (or 0 for xx->3/2)
A technique that I often employ is to substitute all variables at the
same time by enclosing all the replacements inside curly brackets.
BesselJ[xx, yyy]/.{xx->1.5,yyy->0.}
This may help with your "problems with Bessel and Legendre" function
evaluating differently.
Adam Smith
Ariel sumeruk wrote:
> 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