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MathGroup Archive 1997

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Re: Re: Just another bug in MMA 3.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7637] Re: [mg7491] Re: [mg7431] Just another bug in MMA 3.0
  • From: Alistair.Windsor at vuw.ac.nz (Alistair.Windsor at vuw.ac.nz)
  • Date: Fri, 20 Jun 1997 16:16:10 -0400 (EDT)
  • Organization: Victoria University of Wellington, New Zealand
  • Sender: owner-wri-mathgroup at wolfram.com

In article <5nqru3$l5j at smc.vnet.net>, koehler at math.uni-bonn.de (Kai
Koehler) wrote:

> In article <5nfpv3$5qp at smc.vnet.net>, Paulo Mouat
<mouat at mail.telepac.pt> wrote:
> 
> > Kai Koehler wrote:
> 
> > > Sum[Sum[Log[Log[k+j]],{k,1,n}],{j,1,5}]
> > > 
> > > gives
> > > 
> > > 5*Sum[Log[Log[k + j]], {k, 1, n}].
> 
> > If you want to do a multiple sum, the input should read
> > 
> > Sum[Log[Log[k+j]],{k,1,n},{j,1,5}]
> > 
> > What you have typed is a simple sum over k with a function that has an
> > unknown j.  The j on the outer Sum is a dummy variable, with no
> > relation to the one in Log[k+j].
> > 
> > This is not a bug.  Mathematica simply interpreted what you did type,
> > which is not quite what you intended to do.
> 
> If this where true,

It is.

> Sum[Sum[j,{k,1,n}],{j,1,5}]
> 
> should give 5 n j as output. 

No have a look at what he typed again. =>Sum[Log[Log[k+j]],{k,1,n},{j,1,5}] <=.
Here both iterator variables appear in the outer level of the Nested Sums.
In what you hve typed they appear in separate levels.  If you were to
write Sum[Sum[j],{k,1,n},{j,1,5}] you would indeed get 5 n j. There is no
bug here. The iterator j is a local variable assign a unique hash and is
hence different from the j inside the sum.

>Instead you get 15 n (correctly, IMHO).
> Also, in StandardForm, the difference between

-- 
Alistair Windsor
Mathematics Graduate Student 
Victoria University of Wellington
New Zealand


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