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MathGroup Archive 2005

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Re: Strange "not a symbol or valid symbol name" error

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60217] Re: Strange "not a symbol or valid symbol name" error
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Thu, 8 Sep 2005 04:52:55 -0400 (EDT)
  • References: <dfm86d$hek$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Flip wrote:
> Greetings all, I'm using Mathematica 5.0 and have been getting a
> strange error message:
> 
> Unique::usym :
> 10000000000 is not a symbol or a valid symbol name
> 
> This comes from the following integral:
> 
> Integrate[E^(-x) Sqrt[x^2-9], {x,3,5}]
> 
> The limits of integration don't matter much so long as they keep the
> integrand real.
> 
> I don't understand this and am not quite sure how to fix the problem.
> (It's a well defined definite integral, right? It's real in the domain
> of integration and nondivergent.)
> 
> Thanks,
> Flip
> 
Hello,

I tested your integral at 5.1 and it works fine. I don't think the 
difference is in the version, however, I think you assigned x to a 
variable some time before you executed this integral. This is obviously 
a very easy mistake to make, and I have two suggestions:

1)  If in doubt about a strange diagnostic, and if you will not waste 
some important results, try killing the kernel and repeating the 
relevant command(s).

2)  Try to avoid assigning values to useful variables like x. If you 
have an expression and you want to substitute x with 100 (say) use

expr /. x->100

David Bailey
http://www.dbaileyconsultancy.co.uk



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