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

MathGroup Archive 2012

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

Search the Archive

Re: Manually tell Mathematica how to evaluate integrals

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128817] Re: Manually tell Mathematica how to evaluate integrals
  • From: Hui <e.schlemm at hotmail.de>
  • Date: Wed, 28 Nov 2012 03:17:14 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Delivered-to: l-mathgroup@wolfram.com
  • Delivered-to: mathgroup-newout@smc.vnet.net
  • Delivered-to: mathgroup-newsend@smc.vnet.net
  • References: <k8sqlr$ooc$1@smc.vnet.net> <k8uro7$st9$1@smc.vnet.net> <k91u28$5kj$1@smc.vnet.net>

Similar to my first question, I realised that Mathematica can evaluate the integral

Integrate[Log[1 + d Exp[x]],x]

but fails to find the anti-derivative of the function

Log[1 + (d+1) Exp[x]].

I find this quite annoying; does anyone a way around the issue?

Any input is much appreciated.
Thanks, Hui.

Am Dienstag, 27. November 2012 08:38:48 UTC schrieb Hui:
> Thank you DC. There is a typo in my original statement. I meant to suggest that
> 
> 
> 
> x PolyLog[n+1,Exp[x]] - PolyLog[n+2,Exp[x]
> 
> 
> 
> is the anti-derivative of the function
> 
> 
> 
> x PolyLog[n,Exp[x]].
> 
> 
> 
> That seems to be confirmed by differentiating the former expression.
> 
> 
> 
> Any ideas as to why Mathematica won't evaluate this integral, even in the explicit case of, say, n=4?
> 
> 
> 
> On Monday, November 26, 2012 4:40:54 AM UTC, DC wrote:
> 
> > The following doesn't seem to reproduce your statement :
> 
> > 
> 
> > 
> 
> > 
> 
> > Simplify[D[x PolyLog[n + 1, Exp[x]] - x PolyLog[n + 2, Exp[x]], x], 
> 
> > 
> 
> >  Assumptions -> {n \[Element] Integers, x \[Element] Reals}]
> 
> > 
> 
> > 
> 
> > 
> 
> > 
> 
> > 
> 
> > 
> 
> > 
> 
> > On Sunday, 25 November 2012 10:10:17 UTC, Hui  wrote:
> 
> > 
> 
> > > Hi all,
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > I have a question about Mathematica's abilities to solve integrals. There seem to be cases where an antiderivative is explicitly known yet Mathematica fails to compute the integral. One example of this would be
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > Integrate[x PolyLog[n,Exp[x]],x]
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > which Mathematica only solves for n=1,2, even though it is quite easy to find a solution for higher values of n as well, namely
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > x PolyLog[n+1,Exp[x]] - x PolyLog[n+2,Exp[x].
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > I would like to know if it possible to teach Mathematica this integral in such a way that it will also recognise and solve it in more complicated cases such as
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > Integrate[(x+a) PolyLog[n,b Exp[c x]],x].
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > Thank you very much, your assistance is much appreciated!
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > 
> 
> > 
> 
> > > Hui




  • Prev by Date: Re: Numerical expression
  • Next by Date: Help with dynamic functionality
  • Previous by thread: Re: Manually tell Mathematica how to evaluate integrals
  • Next by thread: Re: Manually tell Mathematica how to evaluate integrals