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MathGroup Archive 2003

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Re: NIntegrate and Delayed Functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44150] Re: NIntegrate and Delayed Functions
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 24 Oct 2003 04:24:22 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <bn8eov$nkm$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

is 

D[Integrate[f[x,t],{t,0,z[x]}],x] not

Integrate[D[f[x,t],x],{t,0,z[x]}] + f[x,z[x]] D[z[x],x]

and should you not restrict the values of G[x] to numeric arguments
with G[x_?NumericQ]:= ...
and should you not use ND[] from NumericalMath`NLimit` ??

Regards
  Jens



Mukhtar Bekkali wrote:
> 
> Hi all:
> 
> I have a function f[x,t] which does not have an explicit integral over t,
> only numerical integral exists.  Suppose F[x] is an integral of f[x,t] over
> t where t ranges from 0 to some function r[x].  I need to plot F'[x] or the
> first derivative of F[x] as a function of x (let's call it G[x]).  I tried
> to use Integrate but Mathematica cannot handle it for some functional forms
> of f[x,t] so I am trying to use NIntegrate as a delayed function to speed up
> the evaluation.  However, I receive an error message that the limit of
> integration cannot be z[x] and an empty graph.  Here is the exerpt from my
> code:
> 
> G[x_]:=D[NIntegrate[f[x,t],{t,0,z[x]}],x];
> Plot[G[x],{x,0,1}]
> 
> What am I doing wrong?  Of course all functions,- f[x,t], z[x] have a
> specific form.


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