Re: Sum question and general comment
- To: mathgroup at smc.vnet.net
- Subject: [mg50761] Re: Sum question and general comment
- From: Janusz Kawczak <jkawczak at math.uncc.edu>
- Date: Sun, 19 Sep 2004 21:39:17 -0400 (EDT)
- References: <ci8m99$bpg$1@smc.vnet.net> <ci9b6c$i4n$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Paul, this is neat, but I cannot reproduce your results. For the first sum I am getting 5/(i-2) and other will not evaluate at all. What am I missing? Janusz. Paul Abbott wrote: > In article <ci8m99$bpg$1 at smc.vnet.net>, > Steve Gray <stevebg at adelphia.net> wrote: > > > I don't want to overload the group with my questions, so I only post after > > not being able to find the answer in the Help or at the site. Part of the > > problem of course is that it isn't clear how to state the question so that > > I can look it up*. Anyway, the current question has to do with Sum and > > similar "indexed" operations: > > > > I find no way to do, for example, > > "Sum over i=1 to 100 except i!= 23 and 36", etc., > > There is a way to do this (posted to MathGroup in February this year): > use the Notation package to define your own input notation that accepts > a lower limit of the form, say i != 1 = p. See > > http://physics.uwa.edu.au/pub/Mathematica/MathGroup/TestSumIterator.nb > > > or Sum over values belonging to a list, such as > > "Sum over i (belonging to) {1,2,3,5,7,8,21}", etc., > > In this case, the most natural operation is to use Map. It is not too > hard to implement your own notation for this using Element. > > > "Sum ( i=1 to 10) Sum (0ver j=1 to 10 but j !=i)", etc. (this can be > > awkwardly done with j=1 to i-1 and j=i+1 to 10) > > In some cases there can be workarounds using things like > > (1- KroneckerDelta[i,j]), etc., but these can get complicated and obscure. > > No matter what notation you define, internally the computation will > likely have to use constructs such as this. The point is that you would > like Mathematica to form these constructs automatically and, most > likely, hide them from view. > > > * Someone who makes major progress on the problem of letting users > > communicate with a computer in ordinary, appropriate technical "people" > > language will have big success. > > Personally, I think the Notation package is a tremendous step in this > direction. > > > Part of the answer would be a greatly expanded index, compiled knowing what > > terms people are likely to use for their questions. > > Uniform notation (or notation conversion is required) also. > > Cheers, > Paul > > -- > Paul Abbott Phone: +61 8 9380 2734 > School of Physics, M013 Fax: +61 8 9380 1014 > The University of Western Australia (CRICOS Provider No 00126G) > 35 Stirling Highway > Crawley WA 6009 mailto:paul at physics.uwa.edu.au > AUSTRALIA http://physics.uwa.edu.au/~paul