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MathGroup Archive 2001

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Re: Strange error message from NIntegrate

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28178] Re: Strange error message from NIntegrate
  • From: Henrik Holm <h.holm at spray.no>
  • Date: Tue, 3 Apr 2001 02:37:55 -0400 (EDT)
  • References: <9a964c$gtv@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

[BobHanlon at aol.com]

>  You made the power of x a list (brackets vice parenthreses).

Thank you, that seems to be the problem.

>  There are still problems with the numerical integration.  However, you can 
>  
>      - approximate the answer with a finite upper limit of integration
>      - change the number of intervals (GaussPoints)
>      - change the method of numerical integration
>  
>  NIntegrate[x^(3/2)*Exp[-x]*BesselI[3/2,x/2], {x,0, 1000}]
>  
>  1.0030037040845279
>  
>  NIntegrate[x^(3/2)*Exp[-x]*BesselI[3/2,x/2], {x,0, Infinity}, 
>    GaussPoints -> 10]
>  
>  1.0030037040849122
>  
>  NIntegrate[x^(3/2)*Exp[-x]*BesselI[3/2,x/2], {x,0, Infinity}, 
>    Method -> Trapezoidal]
>  
>  1.0030037040847963

Also. thanks for these tips.  How can I ask Mathematica to
show the answer with more than a few digits?  (It seems that 6
digits is standard.)


Henrik Holm


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