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Re: How to enter an integral in a formula and have mathematica *not*

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109000] Re: How to enter an integral in a formula and have mathematica *not*
  • From: gekko <pfalloon at gmail.com>
  • Date: Sat, 10 Apr 2010 06:51:28 -0400 (EDT)
  • References: <hpkgjc$7vn$1@smc.vnet.net>

On Apr 8, 10:01 pm, Jim Rockford <jim.rockfo... at gmail.com> wrote:
> I have a certain integral, part of a larger expression, that can be
> expressed in terms of incomplete gamma functions by Mathematica.  But
> in carrying out the definite integral and forcing it to be written in
> terms of gamma functions, this introduces branch points and other
> unnecessary complications.  I want the integral left alone and
> evaluated numerically, but I still want to express the general formula
> for this large expression with the unevaluated integral in place.
>
> For example, I'd like
>
> f[x_] = (stuff) + int_{0}^{1} (g[s,x]) ds
>
> where the definite integral is expressed in the usual Mathematica
> notation.
>
> What I do *not* want Mathematica to do at this stage is to do the
> integral analytically and write it in terms of special functions.
> Instead, I just want to later make a list of values for  f[x]  and
> have the integral done numerically.
>
> How can I program this?
>
> Thanks,
> Jim

You'll probably get at least a half-dozen replies along these lines,
but just in case: one way to achieve what you want would be to make
the definition of "f" only match numerical values, e.g.

    f[x_?NumericQ] := stuff[x] + Integrate[g[s,x], {s,0,1}]

If it should only match for Integer arguments, you could use
f[x_Integer] := ... instead.

Cheers, P.


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