Re: Re: Just another bug in MMA 3.0
- To: mathgroup at smc.vnet.net
- Subject: [mg7532] Re: [mg7491] Re: [mg7431] Just another bug in MMA 3.0
- From: koehler at math.uni-bonn.de (Kai Koehler)
- Date: Fri, 13 Jun 1997 03:08:46 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
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,
Sum[Sum[j,{k,1,n}],{j,1,5}]
should give 5 n j as output. Instead you get 15 n (correctly, IMHO).
Also, in StandardForm, the difference between
Sum[Sum[Log[Log[k+j]],{k,1,n}],{j,1,5}]
and
Sum[Log[Log[k+j]],{k,1,n},{j,1,5}]
is just the insertion of a factor (e.g. 1) between the two sums:
\!\(?\+\(j = 1\)\%5 1 \(?\+\(k = 1\)\%n Log[Log[k + j]]\)\)
gives a different output then
\!\(?\+\(j = 1\)\%5\(?\+\(k = 1\)\%n Log[Log[k + j]]\)\)
Similarly,
\!\(?\+\(j = 1\)\%5\((\ ?\+\(k = 1\)\%n Log[Log[k + j]])\)\)
gives a different output then
\!\(?\+\(j = 1\)\%5\((\ ?\+\(k = 1\)\%n Log[Log[k + j]] + 1)\)\)
What you wrote is actually what Michael Trott from Wolfram support mailed
me 2 days ago: It's not a bug, it's a feature. This really worries me: If
they do not even recognize a bug when you show it to them, then what can
you expect them to do?
Kai Koehler