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