Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2012

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

Search the Archive

Re: Integration anomaly?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127021] Re: Integration anomaly?
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sun, 24 Jun 2012 04:26:50 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

On 6/23/12 at 4:16 AM, john_szumiloski at merck.com (Szumiloski, John)
wrote:

>I recently was playing around with the function Log[1 + 1 / ( t^n )
>], and exploring positive values of n.  (I have no interest in
>nonpositive or complex n)   In particular, I wanted to look at its
>integral, so I did this: (v8.0.4, Windows XP)

>Integrate[ Log[1+1/(t^n)], { t, 0, Infinity } ]

>which gave:
>
>ConditionalExpression[ -(Pi Csc[Pi/n]), Re[n]<0 ]

I get the same result using

In[7]:= $Version

Out[7]= 8.0 for Mac OS X x86 (64-bit) (October 5, 2011)

>Now I am no analysis expert, but it seems pretty clear to me that
>the integral diverges for negative (real) n.

Not proof but given

In[8]:= Table[NIntegrate[Log[1 + 1/(t^n)], {t, 0, Infinity}],
{n, 5}]

Out[8]= {23233.1,3.14159,3.6276,4.44288,5.3448}

and

In[9]:= Table[NIntegrate[Log[1 + 1/(t^-n)], {t, 0, Infinity}],
{n, 5}]

Out[9]= {5.522502947974294*10^27954,1.104500589594859*10^27955,1.656750884392288*10^27955,2.209001179189718*10^27955,2.761251473987147*10^27955}

it seems clear the integral converges for n<0 and diverges for n>0




  • Prev by Date: Replace, ReplaceAll and If time performace comparition
  • Next by Date: Re: How to make Excel import symbolically
  • Previous by thread: Re: Integration anomaly?
  • Next by thread: NDSolve and multi-cores