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Re: NIntegrate with floating point limits

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28887] Re: NIntegrate with floating point limits
  • From: "Orestis Vantzos" <atelesforos at hotmail.com>
  • Date: Thu, 17 May 2001 04:22:59 -0400 (EDT)
  • Organization: National Technical University of Athens, Greece
  • References: <9dtasf$f7l@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I haven't pinned down the problem exactly yet, but it appears the problem is
not in the limits but in the expression you integrate:
x=1/4; NIntegrate[....,{u , 0 , .25}]; works just fine!
When you use floating point value for x IN the expression you get the
message.
My best guess for now, is that there is a singularity involved and
Mathematica can't locate it when the integrand is defined using fl.point
value for x...
Orestis Vantzos

"Fred Simons" <f.h.simons at tue.nl> wrote in message
news:9dtasf$f7l at smc.vnet.net...
> Dear mathgroup,
>
> Can someone explain why the following integral can only be computed
> numerically with exact limits and not with a floating point limit?
>
> x = 1/4; NIntegrate[ CosIntegral[(x - u)/x + 1] - CosIntegral[1 - (x -
> u)/x], {u, 0, x}]
>
> returns 0.2362;
>
> x = N[1/4]; NIntegrate[ CosIntegral[(x - u)/x + 1] - CosIntegral[1 - (x -
> u)/x], {u, 0, x}]
>
> returns some complaints and no result.
>
> In all cases I met so far, floating points limits in numerical integration
> caused no problems.
>
> Many thanks in advance,
>
> Fred Simons
>
>
>




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