Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: simplifying definite vs indefinite integrals

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90659] Re: simplifying definite vs indefinite integrals
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 18 Jul 2008 04:01:32 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <g5n464$sbm$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

Integrate[a[x] b[y], {y, s, t}] /.
  Integrate[a_*b_, {x_, x0_, x1_}] /; FreeQ[a, x] :>
   a*Integrate[b, {x, x0, x1}]

??

Regards
   Jens

rikblok at gmail.com wrote:
> Hi Mathematica gurus (& sorry if this is a dupe post),
> 
> I'm new to Mathematica and I was surprised to see that it handles
> definite versus indefinite integrals differently. For example:
> 
> In[1]:= indef = Integrate[a[x] b[y], y]
> 
> Out[1]= a[x] \[Integral]b[y] \[DifferentialD]y
> 
> Nice.  a[x] gets pulled out of the integral.
> 
> In[2]:= def = Integrate[a[x] b[y], {y, s, t}]
> 
> Out[2]= \!\(
> \*SubsuperscriptBox[\(\[Integral]\), \(s\), \(t\)]\(\(a[x]\ b[
>     y]\) \[DifferentialD]y\)\)
> 
> But not for the definite integral.  Why?  And how can I make it factor
> out?
> 
> In[3]:= Collect[def, a[x]]
> 
> Out[3]= \!\(
> \*SubsuperscriptBox[\(\[Integral]\), \(s\), \(t\)]\(\(a[x]\ b[
>     y]\) \[DifferentialD]y\)\)
> 
> doesn't work. Nor does
> 
> In[4]:= Simplify[def]
> 
> Out[4]= \!\(
> \*SubsuperscriptBox[\(\[Integral]\), \(s\), \(t\)]\(\(a[x]\ b[
>     y]\) \[DifferentialD]y\)\)
> 
> I can't even remove a[x] manually:
> 
> In[5]:= FullSimplify[def/a[x]]
> 
> Out[5]= \!\(
> \*SubsuperscriptBox[\(\[Integral]\), \(s\), \(t\)]\(\(a[x]\ b[
>     y]\) \[DifferentialD]y\)\)/a[x]
> 
> Suggestions?  Thanks for your help!
> 
> Rik
> 


  • Prev by Date: Re: Using manipulate with PlotDensities
  • Next by Date: Re: Labeled Plot not a Plot?
  • Previous by thread: simplifying definite vs indefinite integrals
  • Next by thread: Re: simplifying definite vs indefinite integrals