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Re: Is it possible to impose a condition on an iterator

• To: mathgroup at smc.vnet.net
• Subject: [mg101553] Re: [mg101499] Is it possible to impose a condition on an iterator
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Fri, 10 Jul 2009 06:43:06 -0400 (EDT)
• Organization: Mathematics & Statistics, Univ. of Mass./Amherst
• References: <200907090552.BAA16854@smc.vnet.net>
• Reply-to: murray at math.umass.edu

In any looping function, the iterator may take the form {i, lis}, where 
lis is an explicit list of values. So in your situation you need only 
construct that list, for example:

   avals = Complement[Range[20], Range[7, 11]];

Then:

   Sum[a^2 - 3 a/(4 a^2), {a, avals}]

Of course you can do the entire thing at once by putting the Complement 
expression that constructs the list directly into the Sum expression:

   Sum[a^2 - 3 a/(4 a^2), {a, Complement[Range[20], Range[7, 11]]}]

Mauro wrote:
> I would like to perform a summation of this type, 
> 
> Sum[a^2 - 3 a/(4 a^2), {a, 1, 20}]
> 
> excluding however some values of the iteratore, I would for instance
> like to exclude the values than to greater of 6 and inferior to 12. Is
> it possible?
> 
> Thanks
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

• References:
  • Is it possible to impose a condition on an iterator of the summation ?
    • From: Mauro <mauro@NONOyahoo.com>